Spontaneous ankylosis of the hip joint is associated with many etiologies, including trauma, infection, hemophilia, and ankylosing spondylitis. Several treatment options exist for degenerative arthritis of the hip in the young, active patient. Surgical ankylosis is an excellent option in select patients. However, it is rarely performed because of advances in other treatment methods, such as hip arthroscopy, surgical dislocation and femoroacetabular osteoplasty, periacetabular osteotomy, hip resurfacing, partial hip arthroplasty, and total hip arthroplasty (THA).
Surgical ankylosis of the hip was first described more than 100 years ago by Heuysner1 and later by Albee.2 The procedure was initially indicated for the management of conditions such as sepsis, trauma, and degenerative osteoarthritis, and it remains a viable option in young patients who are not ideal candidates for other treatment options.3 Hip ankylosis alters the biomechanics of the adjacent joints, including the lumbosacral spine and ipsilateral knee, as well as the contralateral hip and knee. This often results in increased pain and decreased functional capacity several decades after the ankylosis.4–6 Conversion THA has been reported to effectively relieve or eliminate these symptoms, thereby improving overall patient function and satisfaction.
Conversion THA in the ankylosed hip is technically challenging, and most practicing surgeons have limited clinical experience with this complex operation. Moreover, because surgical hip ankylosis is performed with decreasing frequency, opportunities for performing this surgery are expected to decline. With regard to surgical technique, the surgeon must (1) identify and preserve the hip abductor muscles, (2) accurately identify the hip rotation center of the acetabulum, (3) perform concentric reaming of the acetabular bone bed to achieve medialization and sizing of the component, (4) avoid placement of the acetabular cup in an excessively cephalic position, (5) optimize leg length equalization, and (6) restore ideal femoral offset to avoid impingement and instability. Optimization of surgical technique typically results in very good clinical outcomes following conversion THA in the ankylosed hip.
The surgeon should be well versed in the indications and outcomes of hip ankylosis so as to adequately counsel patients on the complexity and expected outcome of conversion THA (Table 1). According to Beaulé et al,4 surgical ankylosis is indicated in young adults with severe monoarticular disease, high activity demands, and minimal preexisting arthritis of the lumbar spine, ipsilateral knee, or contralateral hip.
The optimal positions of the ankylosed hip are 20° to 30° of flexion, 5° to 10° of external rotation, and 5° of adduction.6 Increased hip flexion is better suited to the patient with a desk job, whereas less flexion is more appropriate for the patient who performs manual labor. Ideally, limb-length discrepancy should be <2 cm. Patients treated to these specifications can remain pain free and function at a high capacity for decades. Suboptimal ankylosis positioning may predispose patients to earlier degeneration of adjacent joints, resulting in pain and functional deterioration. Two studies have reported that two thirds of patients experience difficulty with activities of daily living, such as putting on shoes and socks.5,6 Most patients returned to work, but they claimed a decrease in age-appropriate activity level. Moreover, one third of the patients with hip ankylosis experienced difficulty with sexual activity.
Ankylosis of the hip dramatically affects gait as well as the biomechanics and kinematics of the spine and adjacent joints. Gait analysis studies have reported abnormal patterns, including a shortened stance phase as well as a prolonged swing phase on the ankylosed side.7,8 Patients exhibit slower gait velocity and shortened stride length. In addition, there is increased motion of the lumbar spine, increased lordosis with pelvic tilt, and increased stresses in the ipsilateral knee. These changes result in increased loading on the adjacent joints.
The desire for pain relief and functional improvement is the most frequent indication for conversion THA in patients with progressive, disabling pain in the lower back, ipsilateral knee, or contralateral extremity resulting from hip ankylosis. Improvement in pain and function occurs with enhanced hip biomechanics following conversion THA. Persistent limp is a common out-come, and extensive rehabilitation is necessary postoperatively to achieve optimal function.
Long-term follow-up studies indicate that 13% to 21% of patients with hip ankylosis proceed to conversion THA later in life.5,6 In the largest series published to date, Joshi et al9 reviewed the records of 187 patients (208 hips) treated with conversion THA following prior hip ankylosis. Surgical arthrodesis was done in 160 hips for tuberculous arthritis (66); osteoarthritis (34); nontuberculous septic arthritis (21); congenital dislocation (16); fracture-dislocation (16); and slipped capital femoral epiphysis, Legg-Calvé-Perthes disease, or rheumatoid arthritis (7). Ankylosing spondylitis was the diagnosis for all 48 hips with spontaneous ankylosis. A significant difference was noted in time from initial hip ankylosis to conversion THA based on age at the time of spontaneous fusion. Average time from ankylosis to conversion THA was 41 years in patients aged ≤15 years at the time of ankylosis compared with 24 years in patients aged >15 years (P < 0.0001). However, no difference was found between the groups with regard to the age of the conversion THA (mean, approximately 52 years in both).
Hamadouche et al10 reviewed 45 consecutive conversion THAs in 45 patients with ankylosed hips. The mean duration from initial hip ankylosis to conversion THA was 35.7 years (range, 3 to 65 years). The index etiologies for hip ankylosis included tuberculosis in 26 hips, developmental dysplasia of the hip in 9, hematogenous bacterial infection in 5, osteoarthritis in 3, Legg-Calvé-Perthes disease in 1, and unknown in 1. Ankylosis was spontaneous in 20 hips and surgical in 25 (11 intraarticular, 10 extra-articular, 4 combined). Mean age at the time of THA was 55.8 years (range, 28 to 80 years). The indications for conversion THA were low back pain alone (22), ipsilateral knee pain alone (7), and low back pain and ipsilateral knee pain (16). Varying degrees of degenerative arthritis were confirmed radiographically.
On average, patients present for potential conversion THA in their early to mid 50s. They may present with a wide range of etiologies for the ankylosis. Radiographs of adjacent joints often reveal arthritic changes resulting from increased abnormal stresses.
Conversion THA from an ankylosed hip is a complex operation. Careful preoperative planning is paramount to optimize the outcome and minimize complications. A thorough history should be taken, including index etiology and the indications for hip ankylosis, type of ankylosis (spontaneous or surgical), age since the ankylosis, and previous complications (eg, infection, venous thromboembolism, nerve palsy, nonunion, repeat operations). The physical examination should focus on location of the previous incision or incisions, limblength discrepancy, integrity of the femoral and sciatic nerves, vascular status, pelvic obliquity, kyphoscoliosis of the lumbosacral spine, and range of motion and stability of the ipsilateral knee, contralateral hip, and contralateral knee. When available, the original surgical note should be reviewed to confirm indications for the fusion, surgical approach, management of the abductors, and type of instrumentation used.
Functional integrity of the hip abductor muscle is an important prognostic predictor of ambulation following conversion THA. Manual examination may not be useful because of atrophy and lack of motion. Electromyography can be used to determine the potential for muscle innervation.11,12 Particularly in hips without preexisting hardware, MRI may also be useful to determine muscle integrity, fatty infiltration, and size.
Equalization of limb-length discrepancy is important to facilitate ambulation and reduce limp. However, excessive lengthening can result in neurovascular complications. Kim et al13 reported a mean preoperative limb-length discrepancy of 2.6 cm (range, 1 to 6 cm) in 87 conversion THAs performed in ankylosed hips (86 patients). The mean postoperative limb-length discrepancy was 0.7 cm following conversion THA. Kilgus et al14 reported similar results in their study of 41 hips in 38 patients. In their study, the mean improvement in limb-length discrepancy was 2.5 cm following conversion THA to manage ankylosed hips.
Radiographic evaluation should include a routine pelvis and hip series. The location of instrumentation placed for surgical ankylosis should be thoroughly assessed (Figure 1). Judet views of the acetabulum may better delineate the anterior and posterior columns of the acetabulum than routine pelvic and hip views. CT sometimes can provide additional information on the location of the sciatic and femoral nerves as well as on retained hardware that would require removal. Moreover, CT can aid in identifying the extent of the fusion mass and its relationship to vital neurovascular structures. Data from these studies are used to determine the best surgical approach for fusion takedown. It is important that the proper instrumentation be available for device removal. It is also helpful to obtain imaging of the lumbosacral spine as well as of the ipsilateral and contralateral knees.15,16
For patients with hip ankylosis resulting from prior infection, the surgeon should obtain historical records in an attempt to identify the previous infecting microorganism or microorganisms. Preoperative laboratory studies should include white blood cell count, erythrocyte sedimentation rate, and C-reactive protein level. Preoperative hip aspiration may be attempted under radiographic guidance. A magnetic resonance image may be reviewed for persistent foci of osteomyelitis. Intraoperative assessment with histopathology, Gram stain, and nucleated cell count with differential should be done to rule out active infection prior to implantation of the prostheses. If the possibility of persistent sepsis is a concern, a staged protocol can be undertaken utilizing resection and antibiotic spacers, similar to the protocol used in the management of infected THAs.
Use of a radiolucent fracture table may be helpful if intraoperative fluoroscopy is to be used to aid in device removal and to confirm the positions of the fusion mass takedown, the fit and fill of the implant components, and leg length equalization. A radiolucent fracture table also should be used when concern exists for potential intraoperative fracture.
Several surgical approaches have been reported in the past four decades. Many surgeons have recommended the use of trochanteric osteotomy. Hardinge et al17 recommended performing trochanteric osteotomy with the patient in the supine position. Sathappan et al18 advocate the direct lateral approach and trochanteric osteotomy. If trochanteric osteotomy is done, care should be taken to retain a large bony fragment as well as create a corresponding wide femoral bone bed for the reattachment. Trochanteric osteotomy and associated fixation have been well-described in the literature.19
Other surgical approaches have been used that did not include trochanteric osteotomy. Kim et al13 used a posterolateral approach in 87 conversion THAs. Trochanteric osteotomy was performed in only one hip. Use of this approach can reduce the technical challenges and complications associated with reattachment and healing of the trochanteric fragment, particularly in cases involving significant leg lengthening.
The stability of the trochanteric fragment must be assessed during the trial reduction. If predictable and secure reduction of the fragment to the femur is not possible, then femoral shortening should be considered. Several techniques are available for achieving fixation of the trochanteric osteotomy.19 Technique should be selected based on the fragment size, bone quality, and distance of advancement. Wires can be used in cemented and noncemented stem fixation. In persons with weak bone quality and in those who require lengthy advancement for leg length equalization, we generally prefer to use a trochanteric claw with cables.
Regardless which surgical approach is used, the surgeon must ensure appropriate exposure to remove retained instrumentation, adequately define the anterior and posterior columns of the acetabulum, address femoral deformity, and reduce tension on the soft tissues and neurovascular structures intraoperatively. The abductor muscles should be assessed for integrity and contractility. Constraining soft tissues and capsule should be removed or released to allow for exposure and improve hip motion. The junction between the femoral neck and the ilium is most commonly used to determine the level of the femoral neck osteotomy. Fluoroscopy or static radiographs with a marker placed in the bone can be used to confirm the optimal position of the osteotomy. This is important to avoid inadvertent disruption of the structural integrity of the pelvis (Figure 2, A and B). The anterior acetabular rim and the sciatic notch are also helpful landmarks in further validating the borders of the acetabulum.
Once the femur is mobilized following femoral neck osteotomy, the acetabulum must be prepared. It is critical to identify the inferior border of the acetabulum as referenced by the obturator foramen. Occasionally, in particular in persons with spontaneous ankylosis, the transverse acetabular ligament may be present. This ligament serves as another landmark to identify the acetabulum. Other references include the sciatic notch and the anterior superior iliac spine. Fluoroscopy may be helpful to confirm the orientation, direction, and depth of reaming (Figure 2, C and D).
Selection of cup design and fixation method is dependent on the quantity and quality of the acetabular bone. In cases of spontaneous ankylosis, the acetabular bone bed is likely to be of sufficient quantity and good quality (Figure 3). Acetabular bone quantity and quality may be less than ideal, however, especially in cases of surgical arthrodesis to manage posttraumatic etiologies. Cemented cup fixation remains an option in select cases, such as extreme sclerosis associated with radiation necrosis. Fixation stability and durability may be enhanced with the use of additional cup surface modification (eg, hydroxyapatite coating) or cups made of the newer porous metal materials.20,21 No specific data exist with regard to increased effi cacy with such cup designs in THAs in ankylosed hips.
Adjunct screw fixation is recommended to optimize cup stability (Figure 4). Cup designs that allow for a large-diameter femoral head or a constrained device are especially useful to address concerns related to instability.
Careful attention should be paid to cup position in conversion THAs in patients with bilateral ankylosed hips. Kim et al22 reviewed a series of 12 patients with bilateral ankylosis. These patients were found to be at increased risk of suboptimal cup position as a result of pelvic obliquity and the gait abnormalities associated with the contralateral ankylosis. The authors noted that fixed adduction and flexion would tilt the pelvis anteriorly, with the potential for placement of the cup in insufficient anteversion. Conversely, fixed abduction and flexion may result in insertion of the cup in excessive anteversion. Poor cup positioning can result in instability and excessive wear on the bearing surface.
The selected femoral stem design should restore and maximize femoral offset. This can reduce impingement and enhance abductor biomechanics. Additionally, a large-diameter femoral head (≥36 mm) can provide increased range of motion and further decrease impingement. Standard femoral stem designs are adequate in most cases, barring deficiency or deformity of the proximal metaphysis. In cases of abnormal proximal anatomy, modular stem designs with either proximal or distal fixation should be considered.
A long period of rehabilitation is typically required to achieve maximal functional capacity. In persons treated with trochanteric osteotomy, partial weight bearing is recommended for 6 to 8 weeks postoperatively to allow for bony union. Aggressive hip flexor and abductor exercises should be instituted only after the osteotomy has healed completely. Many patients may need to use a cane to reduce limp for an extended period postoperatively, depending on the functional capacity of the hip abductors. Precautions against dislocation, including the use of an abduction brace, may be needed because of the decreased softtissue tension around the THA.
The greatest benefit of conversion THA is pain relief in the surrounding joints and lumbosacral spine. Amstutz and Sakai23 were among the first to report on conversion THA in ankylosed hips. Of the 16 patients treated in their study, 13 had spontaneous ankylosis. Fifteen patients reported marked pain reduction. Thirteen patients stated that they would undergo the procedure again. Lubahn et al24 reported on 18 conversion THAs in 17 patients. Prior surgical ankylosis had been done in 14 of 18 hips. Twelve of the 13 patients with preoperative back pain reported complete pain relief following conversion THA. All four patients with ipsilateral knee pain preoperatively reported complete relief following THA. Moreover, 7 of the 10 patients with preoperative contralateral hip pain reported complete relief. The results of these studies indicate that patients with surgical or spontaneous hip ankylosis can benefit from conversion THA.
More recently, Hamadouche et al10 reported less predictable pain relief following 45 conversion THAs in 45 patients. In patients with spinal symptoms preoperatively, low back pain improved in only 49% and remained unchanged in 31%. One patient had progression of low back pain, necessitating spinal surgery. Similarly, although knee pain improved in 22% of patients, it remained unchanged in 11%. An additional 13% of patients reported worsening knee pain that led to total knee arthroplasty. Kim et al13 reported complete or near complete relief of back pain in 81 of 86 patients (87 hips) following conversion THA. However, four of the five patients with residual back pain progressed to subsequent back surgeries. Twenty-eight of 38 patients (74%) with ipsilateral knee pain reported satisfactory pain relief following conversion THA. Four of the 10 patients with residual knee pain progressed to total knee arthroplasty. Patients should be counseled that pain in the adjacent joints may not resolve after conversion THA.
Improvement in walking ability and gait pattern is unpredictable. Persistent Trendelenburg gait following conversion THA has been associated with insufficient restoration of femoral offset and the abductor lever arm. Incomplete recovery and strength conditioning of the abductor and extensor muscles can contribute to gait limitations.
Lubahn et al24 reported on 17 patients treated with 18 conversion THAs. Prior to the conversion, nine patients used no walking aids, two used two crutches, and one used a walker. At 1 year following conversion THA, nine patients used no assistive devices, seven used a cane, and one used a walker. Hamadouche et al10 reported that walking ability continued to improve for 2 to 3 years after conversion THA. At a mean final follow-up of 8.5 years, 23 patients had a normal gait pattern, 16 required a cane for long distances, 5 had a limp and often used a cane, and 1 had a severe limp and always used a cane. Schäfer et al25 reported that in 15 patients treated with THA, 11 were able to walk without restriction. However, a negative or mild Trendelenburg sign was found in eight patients, and seven displayed a moderate or severe sign.
Kilgus et al14 found abductor muscle function to be dependent on the preoperative quality of these muscles and on the restoration of optimal hip biomechanics with implant design and positioning. Hip abductor muscle strength continued to improve for ≥2 years following conversion THA. Benedetti et al26 used gait analysis to demonstrate that patients can recover phasic activity of the gluteus medius muscle following conversion THA. They also documented progressive reduction of pelvic compensation in the coronal and sagittal planes when the hip biomechanics were properly restored with optimal component selection and positioning.
Functional Outcome Assessment
Hamadouche et al10 reported improvement in mean Merle d’Aubigne hip score from 11.3 before conversion THA to 16.5 at final follow-up. The scores reached a plateau by 1 year postoperatively. The hip scores were categorized as excellent in 12 patients (27%), very good in 20 (44%), good in 9 (20%), fair in 2 (4%), and poor in 2 (4%). In the study by Schäfer et al,25 most patients reported that improved ability to sit was the greatest benefit of conversion THA. In fact, all 15 patients in their study reported that they would undergo the operation again. Similarly, Rittmeister et al27 reported that 11 of 13 patients who underwent conversion THA for ankylosed hips were satisfied with their clinical and functional outcome. The mean Harris hip score improved from 55 preoperatively to 87 at a mean follow-up of 45 months. All Harris hip scores were inferior to those in persons who underwent THA to manage osteoarthritis.
Clinical outcome following conversion THA varies based on the age of the index hip ankylosis. Reikerås et al28 documented a positive correlation between older age of the hip ankylosis and better outcome in their study of 55 conversion THAs in 55 patients. Joshi et al9 reported higher functional scores following conversion THA in patients aged >15 years at the time of hip ankylosis. They found no correlation between postoperative hip score and the indications for conversion THA. Hip scores were higher in patients with spontaneous ankylosis than in those with surgical ankylosis.
Previous surgical ankylosis and conversion THA done before age 50 years have consistently been identified as important predictors of and risk factors for implant fixation failure leading to revision surgery. Strathy and Fitzgerald29 were among the first to report a significant difference in THA failure rates as a function of the type of hip ankylosis. Their patient population included 80 conversion THAs done in 74 patients between 1970 and 1974, with a mean follow-up of 10 years. Only one failure occurred in the 20 patients with previous spontaneous ankylosis (5%). In contrast, 20 failures occurred in the 60 THAs performed in patients with a previous surgical ankylosis (33%). Cause of the failures included mechanical loosening in 11, infection in 8, and instability in 1. The rate of failure was especially high in patients who had undergone multiple surgeries prior to conversion THA (12 of 18 hips, 67%). The authors suggested that the high failure rate was the result of the altered proximal femoral geometry, which led to suboptimal component positioning and fixation. Age <50 years was also correlated with a higher failure rate. No correlation existed between the failure rate and the etiology or duration of the ankylosis.
Peterson et al30 reported survival rates of 86% at 5 years and 75% at 10 years following conversion THA. Risk factors for failure were found to be surgical arthrodesis, age <50 years at the time of THA, and length of arthrodesis <30 years. Joshi et al9 reported that the difference in cup survival was correlated to the age of the ankylosis:
[T]he probability of survival of the acetabular component at ten years was higher for the patients who had had an arthrodesis when they were fifteen years old or less (100%) than it was for the patients who had fusion when they were more than fifteen years old (93%); the difference was significant (P = 0.024).
Kim et al13 studied nearly equal numbers of THAs performed with either cemented or noncemented fixation and found no difference in survival rate. With cemented implants, second- or third-generation cementing techniques were used. Mean follow-up was 10.2 years for the cemented group and 9.8 years for the noncemented group. There was little difference in mean age at the time of conversion THA. The mean interval from ankylosis to conversion THA was 28.3 years (range, 10 to 49 years). The implant revision rate was similar for each type of ankylosis, with a rate of 16% in the surgical group and 18% in the spontaneous group. The revision rates were also similar with regard to fixation method, with 17% in the cemented group and 18% in the noncemented group. A 22-mm femoral head was used in all but two hips in the entire cohort. Mean linear polyethylene wear rate was 0.24 mm per year in the cemented group and 0.32 mm per year in the noncemented group. The incidence of combined pelvis and femoral osteolysis was 52% in the cemented group and 58% in the noncemented group.
Kim et al13 reported many complications in their series. Intraoperative complications included one case of pelvic discontinuity, one greater trochanteric fracture, one femoral perforation, and two cases of calcar fracture. Postoperative complications included one trochanteric osteotomy nonunion, four cases of infection, and four dislocations. There were two cases of femoral nerve palsy and one case of peroneal nerve palsy. Joshi et al9 reported 24 complications overall (12%), including 1 fatal pulmonary embolism, 3 cases of delayed wound healing, 5 dislocations, and 15 nerve palsies. Heterotopic ossification was evident in 28 hips. The three hips classified as Brooker class III had no associated functional deficit.
Schäfer et al25 reported complications in 6 of 15 THAs performed after hip fusion, with two instances each of nerve palsy, infection, and mechanical loosening of the femoral stem. Heterotopic ossification occurred in seven patients (five grade I, one grade II, one grade IV). Hamadouche et al10 reported five complications: deep venous thrombosis in two patients; wound hematoma in one, requiring surgical débridement; common peroneal nerve palsy in one; and deep infection in a patient with a history of tuberculosis.
Conversion THA following previous hip ankylosis is a relatively uncommon operation. It is technically demanding, with a high risk of complications, including nerve injuries and hip instability. Durability of fixation is of concern, especially in patients with prior surgical ankylosis and/or aged <50 years at the time of conversion THA. All published series consistently document clinical efficacy of conversion THA in improving pain relief in the adjacent joints and in the lower back. The patient should be counseled to expect an extended recovery period requiring aggressive physical therapy, the potential for persistent limp and pain in the adjacent joints, and the possible need for assistive devices. Moreover, they should be advised that disease progression could lead to the need for surgery in those joints. Improvement in implant design and surgical techniques is expected to lead to increased durability of conversion THAs in ankylosed hips.
Evidence-based Medicine: Levels of evidence are described in the table of contents. No level I or II studies are cited in this article. References 13 and 30 are level III studies. References 5-12, 14, 17, and 20-29 are level IV studies. References 1-4, 15, 16, 18, and 19 are level V expert opinion.
References printed in bold type are those published within the past 5 years.
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30. Peterson ED, Nemanich JP, Altenburg A, Cabanela ME: Hip arthroplasty after previous arthrodesis. Clin Orthop Relat Res