The Hip: Preservation, Replacement, and Revision- THA in AS

hip jointTotal Hip Arthroplasty in Ankylosing Spondylitis


Ankylosing spondylitis (AS) is a chronic inflammatory joint disease affecting the axial skeleton, especially the sacro- iliac joints. It affects more males than females, and the age of onset is usually at puberty. There is a familial predisposition and strong correlation to HLA B27 antigen: the prevalence is approximately 0.1% in control subjects and 4% in relatives,1 and 90% of AS patients carry the HLA B27 antigen.2

Classically, AS starts in adolescent males as an insidious onset of low backache and stiffness, and involvement of the sacroiliac joints. It eventually progresses to affect the entire spine. Up to one third of patients develop peripheral arthritis involving the hip and temporomandibular joint.3 Males tend to have more severe disease of the spine and pelvis, whereas females tend to have involvement of the hip, knee, ankle, and wrist.4 Approximately 20% of AS cases start with arthritis of the limbs before affecting the spine.5

Extraskeletal involvement5 includes anterior uveitis, aortic regurgitation, conduction defects and arrhythmias, renal involvement, and loss of vital capacity of the lungs owing to restriction of costovertebral mobility. Multiple sclerosis and cauda equina syndrome have been reported in patients with AS, whereas spinal cord injuries have occurred with spinal fractures and pseudoarthrosis after minor inju- ries. AS is also associated with ulcerative colitis, psoriasis, Reiter syndrome, and Crohn disease.
Approximately 31% of patients with AS have hip involvement, of which 90% is bilateral.6 Usually, these patients first experience hip pain and stiffness. In late and neglected cases, the hips are completely ankylosed and do not present with pain but with complete loss of hip motion, inability to sit properly, and severe difficulty in walking and climbing stairs.

Spinal disease progression in patients with AS is more prevalent in patients with hip arthritis compared with those without hip involvement.7 Gensler et al. reported that early age of onset of disease was associated with hip involvement.8
Patients with clinical hip involvement had a significantly earlier age of disease onset when compared with patients without hip involvement; 21% of the patients with hip involvement had a juvenile onset of the disease compared with 9% of patients without hip involvement.9 Patients with juvenile onset (i.e., before 16 years of age) of AS were at the highest risk of developing hip disease and subsequent need for hip replacement surgery.9

Because of the severe spinal ankylosis, temporoman- dibular involvement, and respiratory restrictions, total hip replacement surgery in patients with AS presents unique problems that are not encountered in patients undergoing hip replacement surgery for primary osteoarthritis. It behooves the surgeon to appreciate the special problems of these patients before embarking on surgery.




Careful delineation of the extent of disease in patients should include the onset of backache or sacroiliac pain and the progression of symptoms to the entire spine and involve- ment of peripheral joints. Extraskeletal involvement is evalu- ated with special attention to the cardiorespiratory function and effort tolerance of the patient.

Physical Examination

Besides the usual examination of the hip for range of motion, fixed flexion, abduction and adduction deformities, and leg length discrepancies, special attention needs to be paid to the four following joints.

Temporomandibular Joint

Approximately 30%–40% of patients with AS have involvement of the temporomandibular joint with loss of ability to open the jaws wide. This disability can create difficulty with oral intubation during general anesthesia. In addition, dental clearance before hip replacement surgery may be compromised with temporomandibular joint involvement.

Cervical Spine

Ankylosis of the cervical spine will make oral intubation difficult, especially in the presence of concomitant temporo- mandibular joint stiffness. In some patients, the trachea can be stiff and more liable to tears during difficult or traumatic intubation because of involvement of the temporomandibular joint and cervical spine. It is best that an experienced anes- thesiologist be present during the induction of general anes- thesia to ensure patient airway safety. Awake fiberoptic nasal intubation would be the best and safest option for general anesthesia in such patients.

Respiratory Function and Chest Excursion

Ankylosing spondylitis can cause costovertebral stiffness resulting in decreased chest excursions, loss of vital capacity, and functional residual capacity. There can also be loss of lung compliance, chronic obstructive pulmonary disease, and upper lobe lung fibrosis. These can result in postopera- tive atelectasis and chest infections.
Thoracic and Lumbosacral Spine

Thoracolumbar deformities can occur with kyphosis affecting cardiorespiratory function. A stiff ankylosed spine with fibrosis and calcification of ligamentum flavum and interspinous ligaments would make spinal injection and anesthesia much more difficult. Spinal fracture with or without neurological deficits can occur with minor injury in patients with AS because of osteoporosis and spinal fragility. At times, these fractures do not unite but develop a pseudoar- throsis because of the stiffened spinal segments. Involvement of the lumbosacral spine with spinal kyphosis can cause the pelvis to tilt vertically, resulting in an increased anteversion and a more vertical orientation of the acetabulum. This can lead to acetabular cup malalignment during surgery and postoperative dislocations unless the surgeon is cognizant of this particular deformity.


Besides the usual anteroposterior and lateral radiographs of the involved hip joint, a pelvic radiograph in both antero- posterior and lateral views will be helpful to study pelvic tilt and obliquity. Careful attention is paid to evaluate whether there is bony or fibrous ankylosis of the hip joint that will make hip joint exposure and dislocation during hip replace- ment surgery much more difficult. Sometimes CT scan of the pelvis will be needed in complex deformities seen in late and neglected cases of AS with completely fused hips.

Cervical spine radiographs with flexion and extension views, together with open mouth views, will be necessary as part of the preoperative workup for anesthesia purposes to assess the stiffness of the neck and possible difficulty of intubation, if present. Radiographs of the lumbosacral spine to assess the state of the spinal ligaments and presence of lumbosacral kyphosis, which can throw the pelvis into a more open anteverted and vertical position, are necessary and helpful in the preoperative assessment.


A thorough preoperative assessment is essential to eval- uate the severity of the disease, in particular the airway involvement and the extra-articular manifestations of the disease.

The respiratory capacity and reserve of the patient should be assessed and optimized with ventilatory exercises and respiratory physiotherapy.

Dental clearance should be scheduled to eradicate dental infections and to treat any loose teeth in anticipation of diffi- cult intubation in such patients.

Spinal exercises and physiotherapy for the limbs would prepare patients who may have muscle atrophy and weakness as result of widespread skeletal disease and stiffness. Bone mineral density measurement would be helpful to assess the degree of disuse osteoporosis, even in younger patients.

Informed consent especially with difficult intubation and anesthesia should be carefully explained, besides the usual risks and alternatives of total hip arthroplasty.

There is an increase in the risk of infections especially with Mycobacterium tuberculosis in patients taking TNF-α blockers, in particular adalimumab, which causes a long period of immunosuppression.10 Mantoux test and chest radiographs should be obtained exclude tuberculosis.10 Giles et al.11 showed a significant association between infectious complications following orthopaedic surgery and treatment with anti–TNF-α agents. However, den Broeder et al.12 reported that the perioperative continuation of anti–TNF-α agents was not a significant risk factor for surgical wound infections.

Perioperative neurological deficits should be documented. The range of motion of all joints should be assessed to plan optimal positioning of the patient on the operating table. It is important for the surgeon to ascertain the position and tilt of the pelvis during positioning of the patient for surgery to ensure correct implantation of the acetabular component. The extent of preoperative investigations depends on the severity of the disease. The investigation can include echo- cardiography, lung function test, imaging of the cervical spine, and arterial blood gas analysis. In view of the poten- tial for conduction defects, a preoperative electrocardiogram is mandatory. An echocardiogram is required to assess the severity of valvular heart disease associated with AS.10

SURGERY Indications

Hip pain that is not improved with physiotherapy and medication is the prime indication for surgery, as is limita- tion of motion concurrent with pain. In neglected and late presentations, some patients may have completely fused hip joints that are, painless but have severe limitation of activity and leg length discrepancies because of fixed flexion, abduc- tion, and adduction deformities that will need to be corrected with surgery.
As there are often bilateral hip involvement and extensive spinal disease, the only viable option for the hip disease in AS is a total hip replacement. Osteotomies and hip arthrod- esis are contraindicated in patients with AS.

In view of the younger age of patients involved, cement- less hip replacements are preferred though cemented replace- ments have been done previously with varying success. The use of ceramic-on-ceramic bearings may provide increased longevity to this younger group of patients, although this has not been specifically demonstrated. Metal-on-metal articula- tions have been reported to have poor results with complica- tions from adverse reactions to metal debris and should not be used.


The main contraindications to hip replacement are infec- tion of the hip joint and patients with neurologic deficits and poor muscular control of the hips and lower limbs.


Ankylosing spondylitis can present challenges to the anes- thetist because of the difficult airway, cardiovascular, and respiratory manifestation of AS. Spinal and epidural anes- thesia are technically difficult and can result in an increased risk of complications. Convulsions secondary to accidental intraosseous injection of bupivacaine during a caudal block and spinal hematomas following the insertion of an epidural anesthetic have been reported.10

Spinal anesthesia can be difficult to administer in view of the calcification of the spinal ligaments and the stiff- ness of the spine. Hence, subarachnoid block using a lateral approach has been advocated as an alternative to the standard midline spinal puncture when general anesthesia is contrain- dicated.13

There is a significant risk of neurologic injury with any excessive neck extension in patients with chronic cervical kyphosis.10 Neck extension can cause vertebrobasilar insuf- ficiency as a result of bony encroachment on the vertebral artery. Injuries to the cervical spine and spinal cord such as dislocation of C6 vertebra and quadriparesis after an emer- gency intubation have been reported. Fixed cervical flexion deformities limit access to the trachea, and tracheostomy may be impossible.10 Death from a retropharyngeal abscess that resulted from multiple attempts at blind intubation has been reported.14 General anesthesia is best administered through awake endoscopic nasotracheal intubation in view of the stiff temporomandibular joint and kyphosis of the cervical spine.

The anatomy of the hip joint is affected by the pres- ence of lumbosacral kyphosis throwing the pelvis tilt into a more vertical position and presenting the acetabulum in a more vertical and anteverted position. Tang and Chiu15 have reported the hyperextension at the hip in patients with AS. They postulated that this anatomic abnormality could lead to more anteverted and vertical inclination of the acetabular cup during surgery, which might predispose the hip prosthesis to anterior dislocation. Therefore, the usual reference of the native acetabulum for cup positioning may put the acetabular component into an unstable vertical anteverted position.

Patients with a completely fused hip would require a careful femoral neck osteotomy to allow exposure of the acetabulum. In cases of complete ankylosis, it is often diffi- cult to judge the optimal acetabular reaming to prepare the bed for the acetabular cup impaction as the normal land- marks of the acetabulum are obliterated. Intraoperative fluo- roscopy will be helpful to establish the optimal acetabular reaming and cup positioning

Approach and Operative Technique

Total hip arthroplasty for most cases of ankylosing spon- dylitis can be performed in the usual approaches for hip replacement surgery, including the direct lateral, Hardinge, posterior, anterolateral, and anterior approaches. The length of incision would vary with degree of deformity and stiff- ness of the hip joint. Care should be exercised throughout the surgery, as the bone is often osteoporotic from disuse, espe- cially in patients with severe crippling disease and stiffness, to prevent intraoperative fractures of femur and acetabulum or perforation of femur.

When there is spontaneous ankylosis of the hip, the surgery becomes much more difficult and challenging (see Fig. 88-1). Joshi et al.16 reported bony ankylosis in 23% in a series of 181 total hip arthroplasties for AS. Bhan et al.17 reported that 48% of patients undergoing hip replacement for AS had bony ankylosis. Careful preoperative planning is vital to optimize the results and minimize complications of surgery in such cases.18

Functional integrity of the hip abductor muscle is an important prognostic predictor of ambulation following hip replacement for ankylosed hips. Manual examination might not be useful because of disuse muscle atrophy and lack of motion in the hip. Electromyography can be used to determine the potential for muscle innervation and function. Magnetic resonance imaging can be used to determine hip muscle integrity, fatty infiltration, and size.18 Intraopera-
tively, the abductor muscles should be assessed for integrity and contractility.18

The use of trochanteric osteotomy is recommended in the ankylosed hip to improve exposure and visualization of the hip joint. During the trochanteric osteotomy, care should be taken to retain a large bony fragment and create a corresponding wide femoral bone bed for the reattach- ment to reduce the risks of trochanteric non-union. Fixation of trochanteric osteotomy is best done using a trochanteric claw plate system with cables to reduce the complication of trochanteric non-union.

A subsequent careful femoral neck osteotomy would be required to allow access and visualization of the hip joint. The junction between the femoral neck and the ilium is most commonly used to determine the level of the femoral neck osteotomy.18 Fluoroscopy or static radiographs with a marker placed in the bone can be used to confirm the optimal posi- tion of the osteotomy. This is important to avoid inadvertent disruption of the structural integrity of the pelvis.18 The ante- rior acetabular rim and the sciatic notch are also helpful land- marks in further validating the borders of the acetabulum.18

After the femoral neck osteotomy is completed and the femur can be mobilized, attention can be moved to the acetabulum. It is important to define the anterior and poste- rior columns of the acetabulum accurately and to identify the inferior border of the acetabulum as referenced by the obturator foramen to identify the hip rotation center of the acetabulum. A good way to begin is to aim for the center of the osteotomized neck or the head of femur fused in the acetabulum and begin reaming with the smallest size acetabular reamer of 40 or 42 mm diameter. Ream the head of femur until the acetabular reamer is about flushed with the rim of the acetabular bed. A check fluoroscopy with the acetabular reamer in place is done to assess the position, depth, inclination, and anteversion of the reamer. Thereafter, care is taken to perform concentric reaming of the acetabular bed to achieve proper medialization and correct sizing of the component, and to avoid placement of the acetabular cup in an excessively cephalic position.18 This can be checked with fluoroscopy or intraoperative radiograph as needed (see Fig.

In many cases, the transverse acetabular ligament18 or the pulvinar fat may be present; it serves as another landmark to identify the acetabulum position and depth. Bhan et al.17 reported that in 74 of 92 hips, the pulvinar fat was seen during acetabular reaming, indicating the location of the original hip joint. Selection of cup design and fixation method is depen- dent on the quality of the acetabular bone. In most cases of AS, the acetabular bone bed is likely to be of good quality and will do well with a cementless ingrowth cup.

Careful attention should be paid to cup position in hip replacement surgery in patients with bilateral ankylosed hips. Kim et al.19 reviewed a series of 12 patients with bilat- eral hip ankylosis and found that they were at an increased risk of suboptimal cup position as a result of pelvic obliquity and the gait abnormalities associated with the contralateral ankylosis. They noted that fixed adduction and flexion would tilt the pelvis anteriorly, with the potential for placement of the cup in insufficient anteversion. Conversely, fixed abduc- tion and flexion can result in insertion of the cup in excessive anteversion. Poor cup positioning can result in instability and excessive wear on the bearing surface.

On the femoral side, there is often some degree of osteo- porosis. Hence, care should be taken to prevent inadvertent perforation of the femoral shaft during reaming and rasping, and cracking of the medial calcar during implantation of a cementless femoral component. The use of cementless femoral prosthesis is preferred because these patients are young and usually in their thirties or forties. When there is a relative dilatation of the proximal femoral canal compared with the more distal canal of the isthmus region, a modern medial lateral taper cementless design will ensure a better canal fit and fill to ensure initial stem stability for stable bone ingrowth. Modular femoral components such as the S-ROM prosthesis (DePuy) can provide a better match for the altered femoral geometry in some cases with severe femoral neck anteversion as reported by Bhan et al.17

Alternative bearings such as ceramic-on-ceramic articu- lation, which has a lower wear rate compared with metal- on-polyethylene articulation, would be desirable in these younger patients. Patients with AS and stiff spines would potentially place more demands on the hips compared with older patients without ankylosed spines.

Additional Procedures

Bhan et al.17 reported in his series of 92 hips with bony ankylosis using the posterior approach that 12 hips required an adductor tenotomy, 39 hips required iliopsoas muscles released, and 34 required anterior capsulectomy to correct severe contractures.


With cementless hip replacements, patients can be started on touch weight, partial, or full weight bearing immediately postoperatively. Nerve blocks and various analgesic modali- ties to minimize pain will expedite rehabilitation.
A long period of rehabilitation is typically required to achieve maximal functional capacity and hip motion. In patients treated with trochanteric osteotomy, touch weight or partial weight bearing is recommended for 6–8 weeks post- operatively to allow for bony union. Aggressive hip flexor and abductor exercises should be instituted only after the osteotomy has healed completely.18


The usual complications of standard hip replacement are well known and need no further explanation; however, in AS, there is the unique problem of a vertical pelvic tilt secondary to kyphotic lumbosacral spine deformity with resulting ante- version of the acetabulum. This problem can result in place- ment of the acetabular component in a more vertical and anteverted position resulting in hip instability and disloca- tions.15 As alluded to earlier, bilateral hip ankylosis can also predispose to cup malpositioning leading to instability and increased liner wear.19

Other problems after hip replacement in patients with AS include unpredictable gain in range of motion after surgery,20 higher incidence of ectopic bone formation as compared with general population, and re-ankylosis of the joint for those who had prior hip ankylosis.21

Heterotopic ossification after hip surgery can result in hip stiffness and loss of motion after surgery.22-24 This can be minimized with the use of nonsteroidal anti-inflammatory drugs (NSAIDs) or low-dose postoperative hip irradiation with protection and shielding of the cementless hip pros- thesis.


The outcome of hip replacement in AS depends on how well controlled the disease in the patient is managed. With early diagnosis and treatment, including well-supervised physiotherapy exercises and timely surgical intervention, the results of hip replacements in these patients can be as good as those for the primary osteoarthritis in patients of similar age. A careful preoperative assessment and planning would reduce the complications and improve the outcome of surgery in these patients. The use of modern hip prosthesis design, highly cross-linked polyethylene, and ceramic-on- ceramic bearings that have much better wear properties would hopefully prolong the survivorship of the hip replace- ments in these younger patients.

Unfortunately, in many parts of the world where medical care of such patients is less than optimal, some patients present late with severe deformities of both the hips and the spine. This presentation makes hip replacement surgery difficult and challenging, often ending in poorer results.

Bhan et al.17 reported on the results of 92 hips in 54 patients who underwent cementless hip replacements for AS that had bony ankylosis, with a mean follow-up of 8.5 years. The average preoperative Harris hip score of 49.5 improved to 82.6 postoperatively. All patients had no hip motion or pain preoperatively. Postoperatively, 10 hips had mild to moderate pain. The mean postoperative sum range of motion at the final follow-up was 156.2 degrees. Preoperatively, 29 patients(54%) could not walk. Post- operatively, all were able to walk and 48 patients (90%) could walk without aids. Heterotopic ossification was seen in 12 (13%) of the patients with no re-ankylosis. Kaplan- Meier survivorship analysis with revision as the end point revealed 98.8% survival at 5 years and 85.8% survival at
8.5 years follow-up.

Sochart et al.25 reported on the long-term results of 43 cemented total hip replacements in 24 patients with AS at a mean follow-up of 22.7 years. All patients had improvement of function and range of motion of the joint. Twenty-one patients (88%) were completely free of pain, whereas the remainder had only slight discomfort. Ten acetabular compo-
nents and one femoral component were revised because of aseptic loosening, and one patient had a revision of both components because of late deep infection. The average time to revision was 13.3 years. Six hips (14%) had minor hetero- topic ossification, and none had clinically important ossifica- tion. Survivorship of the femoral component was 91% at 20 years and 83% at 30 years. The probability of survival of the acetabular components was 73% at 20 years and 70% at 30 years.


Y.S.P., a 35-year-old Chinese man with AS for 18 years, presented with bilateral ankylosed hips, sacroiliac joints, and spine (Figs. 88-1 and 88-2). He had no pain in both the hips and spine, but had severe limitations of daily activities. He was able to walk only for short distances. He was unable to sit comfortably because his hips were fused in extension. On gait evaluation, it was noted that he walked on his toes, likely secondary to the fact that he had no hip motion to allow for normal gait. He had only some occipital cervical motion, and the rest of his spine was completely stiff from his neck to sacrum. His upper limbs were normal. Both hips were fused with no motion. Knee and ankle motion was normal.

Anteroposterior radiograph of pelvis Lateral radiograph of lumbosacral spine
FIGURE 88-1. Anteroposterior radiograph of pelvis of patient with ankylosing spondylitis with bony ankylosis of both hips and sacroiliac joints. FIGURE 88-2. Lateral radiograph of lumbosacral spine of patient with ankylosing spondylitis showing complete anky- losis of spine.

The right hip was done first through a Hardinge direct lateral approach with the patient in the lateral position. The femoral neck was exposed and protected with Hoffman retractors. A careful femoral neck osteotomy was performed to take down the hip ankylosis and expose the hip joint. Next, the acetabulum with the in situ ankylosed femoral head was carefully reamed. The pulvinar fat at the floor of the orig- inal acetabulum was present at the end of the careful serial reaming. Using the acetabular reamer as a guide, an intraop- erative radiograph was taken to assess the intended acetab- ular cup size, position, and depth (Fig. 88-3). When these criteria were judged to be optimal, the definitive cementless acetabular cup (PSL, Stryker, Mahwah, NJ) was press-fit with three screws used for augmentation of the cup stability and a polyethylene liner inserted.

The femur was reamed and rasped in the conventional manner, and a cementless proximally coated femoral component (Omnifit, Stryker) was press-fit after testing trial components for leg length equality and hip stability. The appropriate femoral head was impacted, and the hip was reduced and checked for stability.

Postoperatively, rehabilitation was started, and the left hip replacement was performed approximately 4 months later in a similar fashion. He achieved excellent function with good range of hip motion (Figs. 88-4 through 88-6).
He had revision of the right hip polyethylene liner and bone grafting of the osteolysis of greater trochanter 14 years after index surgery when he complained of mild ache in his right hip. A radiograph showed polyethylene liner wear and localized osteolysis in the greater trochanteric region but no evidence of component loosening (Fig. 88-7). The left hip replacement is still well functioning with no pain after 21 years (Fig. 88-8).


•    Refer patients to an experienced anesthesiologist who is familiar with difficult airway management and spinal anesthesia.

•    Perform a careful preoperative assessment of the deformities of the pelvis and spine to preempt placing the hip components in an unstable position especially in the ankylosed hip.

•    Have intraoperative fluoroscopy and additional surgical equipment for trochanteric osteotomy and fixation, and intraoperative fractures fixation avail- able on standby.

Intraoperative radiograph of right hip after bilateral total hip arthroplsdty
FIGURE 88-3. Intraoperative radiograph of right hip
joint during total hip arthroplasty. After the acetabulum
was tentatively reamed, the last reamer used was left in the
acetabulum, and the radiograph was obtained to assess
the cup position, depth, inclination, and anteversion before
implantation of defi nitive acetabular cup.
FIGURE 88-4. Anteroposterior radiograph of pelvis after
bilateral total hip arthroplasty in a patient with ankylosing
spondylitis with bilateral ankylosed hips. The calcar of the
left femur was cracked during the femoral neck osteotomy,
but healed well after a simple calcar wiring.


ankylosing spondylitis with completely ankylosed spine anky- losing spondylitis squatting completely after bilateral THAs

FIGURE 88-5. Postoperative picture of patient with ankylosing spondylitis with completely ankylosed spine and hips that demonstrate the ability to flex the hips to 90 degrees after bilateral total hip arthroplasty. He had no motion in both hips and spine preoperatively. Notice the completely straight back.

FIGURE 88-6. Postoperative picture of patient with anky- losing spondylitis squatting completely after bilateral THAs. This is an important posture in the Asian culture for work, toilet needs, and prayers.

arthroplasty showing superolateral wear of the polyethylene liner arthroplasty fixed bilateral
FIGURE 88-7. Anteroposterior radiograph of right hip
14 years after total hip arthroplasty showing superolateral wear of the polyethylene liner and localized osteolysis at the greater trochanteric region. There is no evidence of femoral stem or cup loosening.
FIGURE 88-8. Anteroposterior pelvic radiograph 21 years after total hip arthroplasty (THA) demonstrating well-fixed bilateral THA with no signs of loosening. There is some polyethylene liner wear of the left THA and local- ized osteolysis at superolateral corner of left acetabular cup, but the patient is asymptomatic with no pain and continues with regular, yearly follow-up.


•    Be cognizant of the possibility of hip instability espe- cially anterior dislocation in patients with a kyphotic lumbosacral spinal deformity and concomitant pelvic vertical tilt during surgery. It is vital for the surgeon to position the patient personally before the surgery and to an appreciation of the tilt of the pelvis in rela- tion to sagittal axis of the spine prior to draping. This positioning will guide in the placement of the acetabular component in the right anteversion and inclination.

•    Administer indomethacin or other NSAIDs for heterotopic ossification prophylaxis or consider radi- ation.

•    Intensive and prolonged postsurgical physiotherapy are necessary to restore motion of the hips.


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Citation for AQ1 is missing in the text.

AQ1: Please clarify antecedent. What is “this”? Ossification? stiffness? loss of motion? (“This can be minimized…”) AQ2: Please supply location for DePuy.