CHAPTER 9 The hip
Developmental Dislocation of the Hip (DDH)
This condition occurs in the perinatal period and involves displacement of the femoral head relative to the acetabulum; if untreated it disrupts the normal development of the hip joint which in the long term may lead to joint dysplasia, subluxation with gait disturbance, avascular necrosis, and osteoarthritis. The term ‘congenital dislocation of the hip’ (CDH), now less frequently used, is for the main part virtually synonymous. Note, however, that the contraction ‘DDH’ may be somewhat confusingly used for ‘developmental dysplasia of the hip’.
The term ‘neonatal instability of the hip’ (NIH) is of particular value as it is clearly defined: it describes a condition in which the hip is dislocated, able to be dislocated, or is unstable at examination during the first 5 days after delivery. Similarly, ‘late-diagnosed DDH’ is used to describe a dislocated or dislocatable hip diagnosed after the age of 1 week.
The condition is much more common in girls than in boys (80%) and in the first born; there is a familial tendency, and an increased frequency in those suffering from Down’s syndrome; and there is a well established geographical distribution of the disorder. It is commoner after breech presentations, and it may occur in conjunction with other congenital defects.
A simple test devised by Ortolani in the 1960s was found to show instability in the hips of some newborn children, and it was thought that this instability was directly related in every case to congenital dislocation of the hip. As a result, it was considered that if all newborns could be screened with this test, and treated promptly if instability were found, that the condition would no longer pose a problem. Unfortunately, later experience showed that a number of children who had passed the screening test went on to develop hip dislocations. It also became clear that some unstable hips could resolve without treatment; and that treatment itself (in an abduction splint) was not free from complications (about 10% developing avascular necrosis). When ultrasound screening is added to the clinical examination, there is a dramatic increase in the number of positive results, most of which resolve without treatment.
To accommodate these confusing facts, a number of regimens have been developed. One typical example recommends the following:
Note that in an increasing number of centres ultrasound screening is performed routinely. With this there is a predictable rise in false positives which are weeded out during routine after-care surveillance. It has been shown that this can significantly reduce the need for subsequent surgical procedures, hospitalisation and late presenting cases.
DDH in the Older Child
This must be suspected in any child where there is disturbance of gait or posture, shortening of a limb, or indeed any complaint in which the hip might be implicated. If dislocation of the hip is diagnosed late, treatment is aimed at restoring the hip to as near normal as possible. Each case must be assessed on its own merits, but the general principles of treatment are common to all:
DDH in the Adult
Where treatment in childhood has been unsuccessful, or even where the condition has not been diagnosed, a patient may seek help during the third and fourth decades of life. Symptoms may arise from the hips or the spine. In the hips, secondary arthritic changes occur in the false joint that may form between the dislocated femoral head and the ilium with which it comes in contact. In the spine, osteoarthritic changes are a result of long-standing scoliosis (in the unilateral case), increased lumbar lordosis (in both unilateral and bilateral cases), or excessive spinal movements that occur in walking. In a few cases hip replacement surgery may be considered, otherwise the treatment follows the lines for the conservative management of osteoarthritis of the hips and spine.
The Dysplastic Hip
Hip dysplasia is a condition in which the principal feature is that the femoral head is imperfectly contained by the acetabulum. The slope of the acetabulum is frequently greater than normal, and it may be relatively small in comparison with the femoral head. In early life this may be a major factor in developmental dislocation of the hip, but if the hip does not dislocate it may nevertheless give trouble later in life. In the dysplastic hip the central area only of the femoral head transmits the forces of weightbearing to the acetabulum, increasing the joint loadings and predisposing the hip to osteoarthritis and in some cases instability. The symptoms are those of osteoarthritis of the hip, and they may present during the second and third decades of life. Rapid deterioration is the rule. In the younger patient a Chiari osteotomy of the pelvis, an acetabular shelf operation or a high femoral osteotomy may improve the containment of the femoral head, relieve symptoms and slow the onset of osteoarthritis. In the older patient, replacement arthroplasty may be considered.
The Irritable Hip
In childhood there are a number of conditions affecting the hip which may be indistinguishable in their initial stages. They all give rise to a limp, restriction of movements, and sometimes pain in the joint (irritable hip). Children with this history are admitted routinely and treated by light traction until a firm diagnosis has been made. The commonest conditions responsible for irritable hip are transient synovitis, Perthes’ disease and tuberculosis of the hip.
Transient Synovitis
This is the commonest cause of the irritable hip syndrome. The child presents with a limp, and there is sometimes a history of preceding minor trauma which in some cases at least is coincidental. Raised interferon levels have been found, which suggests that a viral synovitis may often be the cause. There is restriction of extension and internal rotation in the affected joint, but there is no systemic upset and the sedimentation rate is generally normal. Radiographs of the hip sometimes give confirmatory evidence of synovitis, as does ultrasound examination, but no other pathology is usually demonstrable. Aspiration and culture of synovial fluid (which is not routinely performed) generally fail to provide any evidence of bacterial infection. A full recovery after 3–6 weeks’ bed rest is the rule. In a number of cases that have been slow to respond there have been positive faecal cultures of Campylobacter, and it is advised that this examination be performed routinely.
Perthes’ Disease
In this condition there is a disturbance of the blood supply to the epiphysis of the femoral head, so that a variably sized portion undergoes a form of avascular necrosis. The cause is unknown. It is five times commoner in boys than in girls, and in 12% of cases it is bilateral: and when both hips are affected they may be involved simultaneously or with an interval between them. It commonly presents between the ages of 4 and 6, and there is an association with anteversion of the femoral neck.
It usually presents with a limp, frequently accompanied by complaint of vague pains in the region of the hips, thighs or knees. Clinically, Perthes’ disease may be suspected by the history, the child’s age and sex, and by the restriction of rotation in the affected hip. As a rule, radiological changes are well established by the time the child presents with symptoms, and these will confirm the diagnosis. (Ultrasound examination shows capsular distension due to synovial thickening, with both hips being generally affected at the earliest stages (as opposed to the findings in transient synovitis).) A pattern where the age of onset is very late (i.e. over 12) has been described and is noted for its poorer prognosis.
The severity of the condition is dependent on the age of onset and the position and extent of the area of the femoral head involved. When a large part of the epiphysis is affected, there is a tendency to flattening and lateral subluxation of the femoral head; these changes are mirrored by the acetabulum, and the resultant deformity predisposes the hip to osteoarthritis later in life. If there is some doubt regarding the extent of these changes, an MRI scan will allow an accurate assessment. Thereafter, as a guide to management and prognosis, the investigative findings are used in an attempt to grade the severity of the case and form a prognosis. This can be difficult in practice, and the results not always consistent. Systems for the classification of cases of Perthes’ disease have been devised by Catterall (Frames 9.86–9.87), Stulberg et al.,1 Salter-Thompson and Herring (Frame 9.91), and all have their advocates. Most recently a radiological index has been proposed by Nelson et al. (Frame 9.92) to grade these cases.
Half of all cases of Perthes’ disease do well irrespective of any treatment, and this is especially the case in the younger age groups (i.e. under 6). Cases which have their onset in the older child, particularly over the age of 9, generally do badly. The long-term results are dependent on the growth of the femoral head, and it is unfortunately the case that treatment has not been shown to materially affect this, or to influence the ultimate outcome. Nevertheless the aims of treatment can be clearly summarised as the relief of symptoms, the containment of the femoral head, and the restoration of movements. It is accepted that in all cases the acute symptoms of pain and severe restriction of movements should be treated by bed rest and traction, followed by physiotherapy. In mild cases, where the prognosis by grading is judged to be good, no further treatment (apart from prolonged observation) is generally advocated, although some prescribe weight-relieving measures for a further period of some months to reduce the chances of weight-bearing stresses leading to further deformation of the femoral head. The results of intervention in those cases judged to carry a poor prognosis are perhaps less clear. The lines of treatment frequently advocated aim at improving the congruity of the femoral head and acetabulum, and improving the effective range of movements in the hip (e.g. by a varus osteotomy of the femoral neck, or a Salter innominate osteotomy).
Tuberculosis
Tuberculosis of the hip remains rare in the UK. The affected child walks with a limp and often complains of pain in the groin or knee. Night pain is a feature. Hip rotation becomes limited, a fixed flexion deformity develops and muscle wasting occurs. Radiographs of the hip in the early stages show rarefaction of bone in the region of the hip and widening of the joint space. As the disease advances there is progressive joint destruction, with abscess formation and sometimes dislocation. The diagnosis is usually confirmed by histological and bacteriological examination of synovial biopsy specimens, or by bacteriological examination of the aspirate.
In early cases complete resolution may be hoped for by antituberculous therapy, bed rest and traction. In the advanced case, joint debridement is carried out with efforts to obtain a bony fusion of the joint.
Acute Pyogenic Arthritis of the Hip
Staphylococcus is the organism most frequently responsible for acute infections in the hip joint. The infection is blood-borne and the diagnosis seldom difficult. The onset is rapid, with high fever and toxaemia. All movements of the hip are severely impaired and accompanied by great pain and protective muscle spasm. The most important diagnostic features distinguishing it from synovitis are fever and elevation of the ESR and C-reactive protein.
The organism responsible may be isolated by blood culture or joint aspiration. Treatment is by use of the appropriate antibiotics in doses large enough to obtain high local concentrations. Bed rest and immobilisation are also essential.
Slipped Femoral Epiphysis
This is a disease of adolescence and is commoner in boys than in girls. The attachment of the femoral epiphysis to the femoral neck loosens, so that the head appears to slide downwards on the femoral neck, giving rise eventually to a coxa vara deformity of the hip. The cause is unknown. In a number of cases there is a history of preceding trauma. A striking feature, however, is that in a high proportion of cases there is the suggestion of a hormonal disturbance. Many are fat, having the appearance of those suffering from the Frölich syndrome. Some cases have been noted to occur in association with hypothyroidism. The condition is frequently bilateral (25% at first presentation, rising later to 60%), and it is essential that the contralateral hip be kept under careful surveillance, particularly during the first 3 months.
Pain may occur in the groin or knee, and if the onset is very acute weight-bearing may become impossible. There is usually restriction of internal rotation and abduction in the affected hip. The diagnosis is confirmed radiographically, the earliest changes being seen in the lateral projections. Late complications of slipped femoral epiphysis include avascular necrosis of the femoral head and chondrolysis.
Slight degrees of slip are treated by internal fixation of the epiphysis without reduction. If there is a large amount of acute displacement a gentle reduction may be attempted before fixation, although some are unwilling to undertake this as they are of the opinion that it may increase the risks of avascular necrosis. If the slip is long standing, osteotomy of the femoral neck (to correct the deformity) is often advised. If only one hip is affected, prophylactic pinning of the other is sometimes undertaken, but this is not advocated unless the risks are judged to be especially high.
Primary Osteoarthritis of the Hip
Primary osteoarthritis of the hip occurs in the middle-aged and elderly, and is often associated with overweight and overwork, although in many cases no obvious cause may be found.
Pain is often poorly localised in the hip, groin, buttock or greater trochanter, and may be referred to the knee. There is increasing difficulty in walking and standing. Sleep is often disturbed, and the general health of the patient becomes undermined as a result. Stiffness may first declare itself when the patient notices difficulty in putting on stockings and cutting the toenails.
Fixed flexion and adduction contractures are common, with apparent shortening of the affected limb. In the early stages weight reduction, physiotherapy and analgesics may be helpful; total hip replacement is the treatment of choice if the condition is advanced.
Secondary Osteoarthritis of the Hip
The symptoms of secondary osteoarthritis of the hip are identical to those of primary osteoarthritis. The condition occurs most frequently as a sequel to developmental dislocation of the hip, congenital coxa vara, hip dysplasia, Perthes’ disease, tuberculous or pyogenic infections, slipped femoral epiphysis, and avascular necrosis secondary to femoral neck fracture or traumatic dislocation of the hip.
In secondary osteoarthritis a younger age group is generally involved than in the case of primary osteoarthritis. In the young patient, where it is thought desirable to avoid the uncertain long-term morbidity of total hip replacement, a hip joint fusion may be considered in unilateral cases. Where pain is more a problem than stiffness, McMurray’s osteotomy of the hip may sometimes be of value.
Rheumatoid Arthritis
The hip joints are frequently involved in rheumatoid arthritis. When both hips and knees are affected, the disability may be profound. In the well selected case, replacement of one or both hips may give a striking improvement in the patient’s symptoms and mobility.
Other Conditions Affecting the Hip
Of the rarer conditions affecting the hip joint, the following are not infrequently overlooked:
The following important points should always be remembered in dealing with the hip joint:
Conditions Associated with Total Hip Joint Replacement
Because of the success of hip joint replacement procedures many of these operations have been performed, and complications, which occur in about 5% of cases, are being seen with increasing frequency.
The most widely used replacement is the Charnley low-friction arthroplasty (LFA) or one of its many variants. In this, the socket is formed from high-density polyethylene and the replacement head from stainless steel. Both components are anchored with quick-setting acrylic cement. During the surgical approach to the hip the greater trochanter may be detached to gain better access; if so, it has to be reattached at the end of the operation; this often done with stainless steel wires.
There are a number of other replacements, which vary in the design of the parts, the materials used, and the techniques of their insertion. In some, the components are inserted without the use of acrylic cement, and the surgical exposure may be made without detachment of the trochanter. Where the functional requirements are not expected to be high (e.g. after intracapsular hip fractures in the very elderly) a hemiarthroplasty may be performed, where the femoral head is replaced with a stemmed prosthesis and the acetabulum is not interfered with.
Excluding complications that may arise in the immediate postoperative period, the problems which may subsequently occur may include the following:
1. Dislocation. The stability of the replacement is dependent on the precision with which the components have been aligned during their insertion, the design of the acetabular component (e.g. whether it has a posterior lip), the time that has elapsed since surgery and the degree of violence to which the components have been subjected. After any hip replacement, the fibrous capsule that forms round the artificial joint thickens and strengthens with time, leading to a progressive resistance to dislocation. In the first few months following surgery a badly aligned joint may dislocate under comparatively minor stress; in other cases, and at a later stage, considerable violence may be necessary. If dislocation occurs, weightbearing suddenly becomes impossible and there is usually marked pain. The limb shortens and may be externally rotated. The diagnosis is confirmed by X-ray examination. Treatment is by reduction (which occasionally needs to be an open one), usually followed by a period of traction until the hip becomes stable. In those cases where there is a major problem of component malalignment, a revision procedure may have to be considered should the dislocation recur.
2. Component failure. Socket failure is rare, but the stem of the femoral prosthesis may occasionally fracture. This is most likely when the patient is overweight or the component has a varus alignment, or loosens. Generally there is immediate loss of the ability to weightbear, and replacement of the fractured component becomes essential.
If the greater trochanter has been reattached with wires, these may fracture and fragment, giving rise to local discomfort and sometimes episodes of sharp, jagging pain. This may be treated by removal of the broken wires. The trochanter itself may fail to unite and may displace. This may cause local discomfort and a Trendelenburg gait. Normally there is slow, spontaneous improvement, but in the early case where the fragment is large and displaced, reattachment may be considered.
3. Fracture of the femur. The femur may fracture (as it may do without the presence of a stemmed prosthesis) as a result of direct or indirect violence, e.g. from a fall. In other cases the forces responsible for the fracture may be less than normal. The presence of the prosthesis considerably reduces the total elasticity of the femoral shaft, giving rise to high stress concentrations in the region of the tip of the prosthesis (one of the commonest sites of fracture); the bone may also be weakened by fretting at the cement–bone interface (where there may be abrasive particle formation), by cystic changes, and by infection (which may be chronic and low grade).
Treatment is dependent on many factors, including the site and pattern of the fracture, its cause, and the general health of the patient, but in the majority of cases further surgery will usually be advised.
4. Component loosening and infection. When this occurs, it is usually at the interface between the cement and bone. It is commonest in the area of the femoral stem, although both components may be affected. The complaint is of pain and impairment of function, and the diagnosis is usually made on the basis of the radiological appearances. Loosening may be the result of infection; in some cases this may be frank, and in others, organisms of low pathogenicity may be found in the affected area. In many cases, although an element of infection may be strongly suspected, no organism can be found and an alternative cause may be sought. In many, loosening may be associated with particulate wear debris, and in others tissue sensitivity to the metallic elements of the components of the prosthesis has been blamed.
Infection may be introduced at the time of the initial operation and grumble on thereafter, leading to loosening, bone absorption, and distal migration of the femoral component. There may be flare-ups accompanied by more acute pain, malaise, and sometimes abscess formation. In other cases, it would seem that late infections may arise as a result of infection being bloodborne from a septic focus elsewhere.
The treatment of these complications is highly specialised. In the (uncommon) case of secondary infection, investigations by blood culture and aspiration, immobilisation, and the prompt administration of the appropriate antibiotics may occasionally lead to resolution. In the case of loosening without the discovery of any organism, a revision procedure may be advised. Where there is evidence of a low-grade infection, a very thorough debridement under antibiotic cover, followed by the insertion of a fresh prosthesis of a pattern designed to accommodate any migration or loss of bone stock, may be attempted (either as a one- or two-stage procedure). Additional measures to control recurrence of local infection may include the use of antibiotic-loaded cement. Where infection is well established, removal of the components and cement may be the only solution which will allow the infection to be overcome, even though limb function will obviously be seriously compromised. In some of these cases, however, once the infection has been eradicated a further replacement procedure may be contemplated.
Assessment of Hip, Knee and Lower Limb Function
For over 50 years attempts have been made to devise a system whereby overall lower limb function might be assessed, so that the extent and progress of any disability might be assessed and the results of surgery evaluated. Over 80 rating systems have been suggested, but unfortunately the lack of standardisation has in many cases prevented the direct comparison of reported series.
There is general agreement on the basic functional parameters which should be assessed. These include pain, stiffness and the ability to perform certain activities of daily living. In some systems there is also inclusion of social and emotional factors (such as the return to work and any noted restrictions), joint movements and X-ray appearances. There have been problems over the weight placed on each of the items assessed, on how to evaluate subjective findings such as pain, and how to reduce systems to manageable levels: many have been abandoned because of their complexity and time involved in their analysis. The presently popular WOMAC (Western Ontario and McMaster Universities Osteoarthritis)2 Index is in fact a self-assessment questionnaire which has been simplified and modified1 to help improve the patient’s assessment of the standard 24 questions asked. It is mainly used to evaluate osteoarthritis and rheumatoid arthritis of the hip and knee, before and after joint replacement therapy. The WOMAC Index is available in 65 alternative language forms and has been well validated.
The initial lower limb assessments were developed specifically for the hip at the time when rapid developments were occurring in hip joint surgery, particularly in the field of joint replacements. The Harris System,3 although frequently modified, has stood the test of time. In it, a normal hip is rated as scoring 100 points, while the hip being examined is described as being so many percent of this theoretical normal. Pain (which is subjective and hard to assess with accuracy) is allocated 44 points. Function, which is highly detailed, is broken down into gait, the use of supports and activities, and merits 47 points. Range of movements attracts only 5 points, and absence of deformity 4 points.
If a hip scoring system is being used to assess the results of a hip replacement (and this is one of the commonest indications), then it is desirable to include details of the radiographic appearances which are so important. The terminology has been described as standard and unalterable in its definition, so that without weighting results can be readily compared between series. Although use of the full list (described in the reference) may have to be considered where publication is intended, the questions in the clinical assessment are of such value in assessing any case that they are appended here.
