Oxford Textbook of Trauma and Orthopaedics (2 edn)
Annotate
Cite
Summary points
Hip Dysplasia
Despite screening programs, a large number of patients are affected by dysplastic hips and their sequelae
An understanding of anatomical abnormalities is crucial
Appropriate techniques and implants make arthroplasty feasible
Complications are significantly higher than standard primary hip replacements
Protrusio Acetabuli
Technical difficulties include inadequate medial wall and restoring offset, hip centre and leg lengths
Neck may need to be cut in-situ; bone graft is usually necessary and ideally should be taken from the femoral head
Antiprotrusio cages or custom implants may be needed in cases with excessive bone loss
Arthrodesed hip to total hip replacement
Careful evaluation of the gluteal muscles is mandatory and predicts final walking ability and patient satisfaction
Long-term effectiveness of total hip replacement in ankylosed hips is satisfactory but there is a higher complication rate
The dysplastic hip
Introduction
The severity of hip dysplasia varies widely and adults with dysplastic hips pose a number of technical challenges, ranging from the identification and preparation of the true acetabulum, preparation of the femoral canal, and stable reduction of the components.
Patients who have hip dysplasia are often young and active, and have had previous operations on their hip. Total hip replacement in such patients has been associated with high rates of complications and revision. It is therefore critical to understand the complexities of total hip replacement and to plan any intervention thoroughly.
Anatomy
Acetabulum:
In a low subluxation, the acetabulum is shallow but may have a wide, oval opening
Anteromedially, the wall may be very thin
In a high dislocation the affected side of the pelvis is smaller and the acetabular wall is thin, soft, and in some grossly anteverted
Proximal femur:
Small head and short neck. Usually significantly anteverted
Usually significantly anteverted
Greater trochanter is posterior displaced
Narrow, straight tapered femoral canal with a tight isthmus
Increased neck-shaft angle
Soft tissues:
Shortened hamstrings, adductors, and quadriceps
Horizontal orientation of the abductors from proximal migration of the femoral head
Thickened hip capsule
Shortened sciatic nerve, vulnerable to lengthening
Altered normal course of femoral nerve and profunda artery.
The distorted anatomy of the proximal aspect of the femur, which includes excessive anteversion of the femoral neck and posterior displacement of the trochanter. (Reprinted with permission from Haddad, F., Masri, B., Garbuz, D., and Duncan, C. (1999). Primary total hip replacement of the dysplastic hip. Journal of Bone and Joint Surgery, 81A, 1462–82.)
Posterolateral view of a congenitally dislocated hip. The femur is riding high against the false acetabulum at a thin portion of the upper ilium; the femoral neck is markedly anteverted and smaller than usual. A true acetabulum is present but poorly developed. Reprinted with permission from Amstutz, H. (1991). Hip Arthroplasty. New York: Churchill Livingstone.
Assessment
Common symptoms and signs include:
Pain
Limb-length discrepancy
Limp
Referred knee pain
Abductor lurch
Compensatory lumbar lordosis
Positive Trendelenburg sign.
Classification
Crowe and colleagues classified dysplastic hips radiographically into four categories depending on the extent of femoral head proximal migration. The Crowe classification system is the simplest and most widely used and allows comparison of operative techniques.
Grade 1:
Proximal displacement less than0.1% of pelvic height or less than 50% subluxation of the height of the femoral head
Grade 2:
Displacement of 0.10–0.15% or subluxation 50–75% of the height of the femoral head
Usually do not have leg-length inequality or loss of bone stock
With low dislocation, the femoral head articulates with the false acetabulum which partially covers the true acetabulum; on x-ray there may be two overlapping acetabula
Inferior part of the false acetabulum is an osteophyte which is located at the level of the superior rim of the true acetabulum; visible part of the true acetabulum can therefore be missed
Grade 3:
Displacement of 0.15–0.20% or subluxation of 75–100% of the height of the femoral head
Complete loss of superior acetabular roof
May have thin medial wall; anterior and posterior columns are intact
Grade 4:
Displacement greater than 0.20% or subluxation greater than 100% of the height of the femoral head
True acetabulum is deficient but remains recognizable
Radiograph showing measurements for the Crowe classification system. A) Vertical distance between the reference interteardrop line (line 1) and the head-neck junction (line 2); B) vertical distance between the line connecting the ischial tuberosities (line 3) and the line connecting the iliac crests (line 4).
Patients with Crowe grade 2 or grade 3 tend to develop degenerative changes earlier and proceed to total hip replacement at a younger age than grade 1 or 4.
Preoperative planning
Previous operations are common and add new surgical challenges. Previous femoral osteotomies make exposure more difficult and the procedure more technically demanding, but without significantly higher complication rates. Periacetabular and pelvic osteotomies may improve acetabular coverage but may alter available bone stock and careful assessment is necessary.
Crowe 1–4 dysplastic hips.
Bilateral Crowe grade 4 hips.
Retained metalwork and hardware can be problematic and its removal may be associated with significant morbidity. Some authors advocate the removal of hardware in the dysplastic hip setting routinely to avoid later difficulties with embedded or even intramedullary metalwork at a later date. In situ metal will need to be removed before a total hip replacement and specialized instruments and equipment may be needed. A staged procedure is sometimes necessary.
Preoperative planning is crucial in achieving a successful outcome. Useful investigations include:
Radiographs
Computed tomography (CT) scan can assess bone stock and degree of femoral anteversion
A magnetic resonance image (MRI) scan can assess laxity of soft tissues around the hip.
Templating
Acetabulum:
Position of true acetabulum should be identified
Need to decide whether to attempt to restore acetabulum to its original location or accept a non-anatomic (high hip centre) position
True acetabulum placement diminishes joint reaction force, facilitates limb lengthening, and improves abductor function
Assess degree of anteversion and adequacy of bone stock
Femur:
Size of the femoral canal
Need for custom components
Need for rotational osteotomy. Consider if anteversion greater than 40 degrees
Need for relative equalization of leg lengths
Restoration of abductor function
Components:
Estimate for size of components
Method of fixation
Need for bone graft
Special or custom made equipment.
The approach
Standard anterolateral or posterolateral approaches can be used with less severe degrees of dysplasia. Transtrochanteric or subtrochanteric approach may be necessary for high dislocation or where abductor retensioning is required. This approach affords excellent exposure at the cost of the difficulties and complications of trochanteric reattachment.
CT scan assessing bone stock and femoral neck anteversion.
Crowe 1 dysplastic right hip pre- and post-uncemented total hip replacement.
Bilateral hip dysplasia pre- and post-bilateral hip replacements.
Dysplastic left hip pre- and post-left total hip replacement with structural superolateral autograft augmentation.
Crowe grade 1 dysplasia right hip and grade 3 left hip. The right hip was more symptomatic and a Birmingham mid-head resection arthroplasty (Smith and Nephew) was performed..
The acetabulum
Obtaining satisfactory acetabular coverage is crucial. At least 70% contact should be with host bone. Either bone graft or cement can be used to fill superior defects.
When there is only a moderate reduction in bone stock, small acetabular components may be used. Sochart and Porter reported 97% 10-year survival and 58% 25-year survival of extra small Charnley acetabular components (38mm or less) usually with 22-mm heads.
Changes in the centre of hip rotation alter hip biomechanics. Acetabular placement can be non-anatomical or anatomical.
Better bone stock at site of true acetabulum
May restore Shenton’s line but acetabular coverage may be limited
Use the transverse ligament as a landmark
Loosening 13% at fifteen years (Linde and Jansen)
May not be possible if hip is very stiff
Uncemented fixation may be advantageous for implant survival but needs good coverage
If acetabular component is small due to limited bone stock 22mm femoral heads can be used
Three alternative techniques that have been used for acetabular reconstruction during total hip arthroplasty in hips with a low dislocation. A) Superior placement of the cup. The cup is placed in the false acetabulum, and the superior location of the centre of rotation of the artificial joint is accepted. B) The superolateral augmentation technique with the use of a structural graft. C) The cotyloplasty technique. Complete coverage and anatomical placement of the cup are obtained with controlled medialization. (Reprinted with permission from Hartofilakidis, G. and Karachalios, T. (2004). Total hip arthroplasty for congenital hip disease. Journal of Bone and Joint Surgery, 86A, 242–50.)
Crowe grade 1 dysplastic right hip pre- and post-uncemented total hip replacement.
Dunn and Hess recommended a deliberate fracture of the medial wall (cotyloplasty) to place the cup within the available iliac bone plus or minus augmentation with a mesh. The defect is then reinforced with autogenous bone graft and a small cup cemented in. This procedure advances the acetabulum medially and shifts the weight-bearing axis distal to the acetabulum, whilst gaining good anterior and posterior coverage (Figure 7.8.6C).
The femur
Anteversion:
Significant anteversion (greater than 40 degrees) may necessitate a derotational osteotomy or the use of a custom or modular implant in which version of the femoral neck can be varied
Femoral shortening:
The femur may need to be shortened to protect the sciatic nerve, especially if the acetabulum is brought down to its true level
Lengthening of 4cm or more is associated with increased risk of nerve damage. Leg lengthening of <4cm—no nerve palsy; lengthening >4cm—28% develop a nerve palsy
Shortening can be carried out at the level of the trochanter or in the subtrochanteric region
Subtrochanteric shortening is indicated when several centimetres of shortening is necessary or if derotation osteotomy required
Femoral neck shortening is combined with release of the psoas and external rotators
Narrow femoral canal and short femoral neck often demands the use of a small, short, straight component. In Crowe grade 1, 2, or 3 a conventional implant can usually be used as long as the size of the femur is taken into account
Distortion from previous osteotomies must be considered.
The abductors
Osteonecrosis and trochanteric overgrowth in dysplastic hips may result in the greater trochanter lying superior to the centre of the femoral head
May be resolved with:
Appropriate femoral component and increased offset
Extensive capsular release, psoas release, gluteus maximus tendon transposition
Abductor slide: stripping abductors off ilium and advancing them on the superior gluteal neurovascular bundle
If the greater trochanter or the abductors cannot be reattached they can be sutured to tensor fascia lata and immobilized in abduction for 6 weeks.
Complications and outcomes
Complications are consistently higher in dysplastic total hip replacements compared with osteoarthritis hip replacements.
Nerve palsy: 3–15% in published series. Maximum lengthening 4cm for dysplastic hips
Dislocation: 5–11%
Trochanteric non-union: 11–29%
Fracture of the narrow femoral canal
Impingement: increased if high hip centre used, particularly if the hip is placed medially. The femoral component impinges on the anterior acetabular column in flexion and internal rotation and impinges on the posterior column in extension and external rotation. Reduced with increased offset and release of rectus femoris
Infection: higher rates reported may be due to longer operating times and more extensive soft tissue dissection and stripping.
Protrusio acetabuli
Introduction
Protrusio acetabuli was first described by Otto in 1824 as an intrapelvic protrusion of the femoral head occurring as ‘an abnormal gouty manifestation’ in adult women.
Protrusio may be primary or secondary and is thought to occur from the result of remodelling of the weak, medial acetabular bone after multiple recurring stress fractures. It is defined as displacement of the femoral head medial to the ilio-ischial line. In the early stages this heals with no apparent bone defect, in later stages the bone is severely fragmented. The deformity may progress until the femoral neck impinges on the side of the pelvis. Technical difficulties are, thus, normally encountered with the medial wall of the acetabulum in total hip arthroplasty.
Primary protrusion (Otto pelvis):
Is characterized by progressive protrusion in middle-aged women
Bilateral in one-third of patients and causes pain and limitation of movement at an early age
Varus deformity of the femoral neck and degenerative changes are common.
Secondary protrusio may be bilateral or unilateral and due to:
Paget’s
Marfan’s
Rheumatoid arthritis
Ankylosing spondylitis
Osteomalacia
Septic arthritis
Central fracture dislocation
Total hip replacement and migration of the femoral head or cup.
Sotelo-Garza and Charnley measured the distance between the medial wall of the acetabulum and the pelvic brim (ilio-pectineal line) radiographically. They recognized sthree grades:
1–5mm (mild protrusion)
6–15mm (moderate)
Over 15mm (severe).
Radiographic diagnosis:
If the medial wall of the acetabulum is 3mm or more medial to the ilio-ischial line in men and 6mm medial to it in women
If femoral head is medial to Kohler’s line (line from medial border of ilium to medial border of the ischium)
If centre edge angle of Wiberg is greater than 40 degrees (normal = 35 degrees).
Kohler’s line and centre edge angle of Wiburg in a normal hip.
Sotelo-Garza and Charnley method.
Preoperative planning
Successful total hip replacement depends upon restoring:
The medial wall
The ‘hip centre’ position
The correct offset and abductor function
Leg length inequality
and preventing recurrent protrusio.
Operative procedure (Figure 7.8.15)
Minor degrees of protrusio can be treated successfully with a standard total hip replacement. Moderate or severe degrees compromise the medial wall and an alternative should be considered. In some cases the neck cut will need to be made ‘in situ’ rather than risking a fracture whilst trying to dislocate the hip.
Bone graft
Bone grafting offers an elegant solution to managing the medial wall defect in protrusio. Various techniques have been described. It needs to be intimately opposed to the irregular host bed and compressible to allow sufficient incorporation and remodelling. Bone wafers meet these criteria better than a single massive graft as described by Heywood in 1980. Wherever possible, bone should be taken from the femoral head and supplemented by cancellous curettings from the femoral neck and greater trochanter. Morcelized bone graft is used for contained defects and can undergo revascularization and remodelling; it strengthens with time. Bone graft also allows cement to be inserted and offers resistance to compression. Using cement alone against the weak medial wall provides poor containment and fixation, which in turn leads to premature loosening.
Acetabulum
Uncemented components can be inserted over the bone graft in a more lateral and anatomic position and secured with acetabular screws. Ideally an acetabular component should contain a peripheral flare, plus or minus peripherally placed screws, rather than a true hemisphere in order to prevent progressive medialization of the component. If a cementless cup is used, contact with host bone should be at least 50%. If contact cannot be made with at least 50% of host bone, then a cemented cup with a reinforcement ring or the technique of cementing into impacted bone should be used. In cases of extensive bone loss, antiprotrusio cages are necessary.
Pre- and postoperative radiographs of primary total hip replacement in primary bilateral protrusio acetabuli.
Reaming
It is essential not to deepen the acetabulum while reaming; the surgeon should ream to allow a good peripheral fit. The reamer can be used in reverse mode to mould and conform the graft to the acetabular floor.
Results
The adequacy of correction of the deformity and anatomical centre of rotation correlates with long-term prosthetic survivorship. Good results exist for grafted hips; cement or antiprotrusio cages alone may fail early and should be supplemented with bone graft to provide lasting support.
Primary protrusio is uncommon and accounts for only a small percentage of cases
Technical difficulties include inadequate medial wall and restoring offset, hip centre and leg lengths
Neck may need to be cut in-situ; bone graft is usually necessary and ideally should be taken from the femoral head
Antiprotrusio cages or custom implants may be needed in cases with excessive bone loss.
Conversion of arthrodesed hip to total hip replacement
Introduction
Hip arthrodesis can successfully provide long-term pain relief and will allow the resumption of manual labour and demanding physical activities. However, over time, it may be associated with a significant functional disability:
Back pain:
Multilevel degenerate changes common
Leg-length inequality and fusion malposition exacerbate lower back pain
Ipsilateral knee pain and instability:
More likely in an adducted fused position
Tendency for valgus deformity
Contralateral hip pain: more likely if hip fused in an abducted position
Painful pseudoarthosis.
Conversion to a total hip replacement may improve these symptoms as well as restoring leg-length inequality and improving hip mobility. Conversion of an ankylosed hip does, however, introduce a number of challenges:
The effect of previous operations on both bone and soft tissues
Atrophy of periarticular muscles
The initial disease and indication for fusion.
Mid-term results have been satisfactory but complications, failures, restricted postoperative motion, and instability are more frequent than after primary hip replacement.
Preoperative planning
Appropriate radiographs:
Anteroposterior and lateral
Judet views may identify anterior or posterior column deficiencies
CT scan to assess bone stock
MRI can be helpful in assessing the proximity of neurovascular structures and abductor muscle mass
Position of fusion: patients with abnormal positions of fusion are more likely to have clinically significant soft tissue contractures and may require further soft tissue releases
Further abductor muscle assessment:
EMG studies: routine use in assessing abductor function may be questionable
Some authors suggest palpation of abductor muscle contraction
Take care in offering conversion to total hip replacement when gluteal muscles are not continuous and the hip is fused in a good position.
Operative technique (Figure 7.8.16)
Numerous approaches have been described. The authors prefer a standard posterior approach although the direct lateral or a transtrochanteric approach is commonly used with success.
Gluteal muscles are assessed and any internal fixation devices will need to be removed. The femoral neck and the site of the fusion between the ilium and femoral head needs to be clearly visualized and preoperative planning is helpful in achieving this. If in doubt, an intraoperative radiograph can be obtained. Heterotopic bone is removed with an osteotome and the femoral neck is cut with an oscillating saw. Adequate exposure is necessary to identify the inferior margin of the acetabulum.
Pre- and postoperative radiographs of conversion of an ankylosed left hip to total hip replacement; a previous right Birmingham resurfacing (Smith and Nephew) has been performed.
Technical considerations
Acetabular component:
Consider constrained liner, especially if poor abductors
Structural grafting is sometimes required
Femoral component: routinely prepared using modular implants to restore soft tissue stability, hip mechanics and a stable reduction
Soft tissues releases are frequently required:
Percutaneous adductor tenotomy
Psoas release
If no abductors, the proximal femur can be sewn to the tensor fascia lata anteriorly and the gluteus maximus and iliotibial band posteriorly.
Postoperative rehabilitation
Routine thromboprophylaxis and prophylactic antibiotics
‘Slings and springs’ until muscle control and then weight bearing depending on the type of implant fixation
If any doubt about abductors, then an abduction brace for 6 weeks should be worn.
Results
The effectiveness of total hip replacement following hip fusion has been demonstrated in a number of series. Back pain is often relieved (70–90%) and leg lengths can be improved. Ipsilateral knee pain is less predictably relieved. Success is often more reliable in patients with spontaneous ankylosis.
Complications
More complications are generally reported than after conventional total hip replacement:
Dislocation:
More common if early fusion (less than 15 years) due to underdevelopment of the abductor muscles
Quoted rates vary from 2–6%
Infection: 2–6%
Nerve palsy: sciatic and femoral 2–13%
Heterotopic ossification:
Up to 13%
Some authors advocate the routine use of non-steroidal anti-inflammatory drugs
Careful evaluation of the gluteal muscles is mandatory and predicts final walking ability and patient satisfaction
Long-term effectiveness of total hip replacement in ankylosed hips is satisfactory
Patients should be counseled about the higher rate of complications
Trendelenburg gait will normally persist but abductor function may improve for up to 3 years.
Other difficult primary total hip replacements
Paget’s disease (Figure 7.8.17)
Characterized by increased bone resorption and secondary formation of abnormal new bone
Deformed proximal femur and hypersclerotic bone are common
Paget’s disease may be incidental or a consequence of Paget’s disease
Degenerative changes in the hip joint are typically in the form of medial joint space narrowing compared to superior joint space narrowing in primary osteoarthritis
If the acetabulum is involved, protrusio may occur in 25–50% of cases
If the femur is involved coax vara and anterior or lateral bowing of the femoral shaft may occur
As the disease progresses, the femur becomes sclerotic, and the intramedullary canal is sometimes obliterated
Potential for serious bleeding perioperatively
Consider cemented arthroplasty
Increased incidence of early loosening and heterotopic ossification.
Postacetabular fracture
Preoperatively:
Ensure no occult deep infection
CT scan to assess bone stock
Assess sciatic nerve carefully
Extensile approach necessary to remove hardware
May encounter altered anatomy
May have large bony defects requiring bone graft and cages
Higher postoperative complication rates because of scarring from previous surgery, retained hardware, and heterotopic bone
Successful results but associated with earlier loosening than total hip replacements for primary osteoarthritis.
Paget’s disease in the right proximal femur and a degenerate left hip.
Slipped upper femoral epiphysis
First described by Mueller in 1889
The displacement of the femoral head usually results in a varus and external rotation orientation between the epiphysis and the metaphysis. When the deformity is severe or there are secondary complications such as chondrolysis or osteonecrosis, secondary osteoarthritis is an early complication
Patients are often young and active and choice of implant is important; total hip replacement should only be considered when all other options have been exhausted.
Ankylosing spondylitis
Preoperative respiratory and cardiac evaluation are necessary
May be difficult to mobilize the hip joint if severe contractures or ankylosis; in situ neck osteotomy may be needed
Uncemented femoral components only if bone is of good quality—often the femur has a ‘stove pipe’ deformity with straight lateral walls, making it unsuitable for press-fit or porous coated stems
Heterotopic ossification only more likely if hip was completely ankylosed.
Osteonecrosis
Osteonecrosis can be idiopathic or secondary to other pathology such as sickle cell disease, alcohol, or steroids
Long-term studies show that patients with osteonecrosis who undergo total hip replacement are up to four times more likely to experience an overall failure from aseptic loosening or infection than those with osteoarthritis.
