 SPINE

Decision making regarding spinal osteotomy and total hip replacement for ankylosing spondylitis EXPERIENCE WITH 28 PATIENTS G. Q. Zheng, Y. G. Zhang, J. Y. Chen, Y. Wang From General Hospital of Chinese People’s Liberation Army, Beijing, China

Few studies have examined the order in which a spinal osteotomy and total hip replacement (THR) are to be performed for patients with ankylosing spondylitis. We have retrospectively reviewed 28 consecutive patients with ankylosing spondylitis who underwent both a spinal osteotomy and a THR from September 2004 to November 2012. In the cohort 22 patients had a spinal osteotomy before a THR (group 1), and six patients had a THR before a spinal osteotomy (group 2). The mean duration of follow-up was 3.5 years (2 to 9). The spinal sagittal Cobb angle of the vertebral osteotomy segment was corrected from a pre-operative kyphosis angle of 32.4 (SD 15.5°) to a post-operative lordosis 29.6 (SD 11.2°) (p < 0.001). Significant improvements in pain, function and range of movement were observed following THR. In group 2, two of six patients had an early anterior dislocation. The spinal osteotomy was performed two weeks after the THR. At follow-up, no hip has required revision in either group. Although this non-comparative study only involved a small number of patients, given our experience, we believe a spinal osteotomy should be performed prior to a THR, unless the deformity is so severe that the procedure cannot be performed. Cite this article: Bone Joint J 2014;96-B:360–5.

 G.Q. Zheng, MD, Spine Surgeon General Hospital of Chinese People’s Liberation Army , Department of Orthopedics, Fuxing Road, 28, Beijing 100853, China.  Y. G. Zhang, MD, Professor  J. Y. Chen, MD, Professor  Y. Wang, MD, PhD, Professor General Hospital of Chinese People’s Liberation Army, Department of Orthopedics, Fuxing Road, 28, Beijing 100853, China. Correspondence should be sent to Dr Y. Wang; e-mail: [email protected] ©2014 The British Editorial Society of Bone & Joint Surgery doi:10.1302/0301-620X.96B3. 32774 $2.00 Bone Joint J 2014;96-B:360–5. Received 20 July 2013; Accepted after revision 6 December 2013

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Ankylosing spondylitis (AS) is a chronic inflammatory disease primarily affecting the sacroiliac joints, spine, hips and, less commonly, the knee joints.1,2 The characteristic spinal deformity is a combination of a thoracic hyperkyphosis and a flattening of the lumbar lordosis, causing the patient’s head and neck to thrust forward. Over time, the kyphotic deformity, resulting from AS, causes a downward and forward shift of the patient’s trunk and this may restrict activities of daily living and cause intra-abdominal complications.3-5 In approximately one-third of AS patients, degeneration of the hips may occur, and among those with affected hips, 90% present with bilateral hip ankylosis.6 Fused hips, loss of lumbar lordosis, and progressive thoracic and cervical kyphosis all contribute to the functionally disabling stooped posture typical of AS patients. The aim of surgical treatment of these patients is to reduce pain and improve function.7,8 Spinal osteotomy and total hip replacement (THR) are the most common surgical interventions.9-13 However, for patients who have both hips affected as well as a spinal flexion deformity, they require two operations; so which procedure should be performed first? Some authors state that correction of deformities of the hips should be carried out before considering

corrective spinal osteotomy.13-18 Others take the opposite view. Tang et al19 used a stereolithographic model to show that the pelvis was extended when patients with ankylosing spondylitis stand up. If an acetabular component is to be inserted anatomically, anterior dislocation of the prosthesis is to be expected. They updated this technique in 2007 and began using three-dimensional computed tomography (CT) reconstructions to demonstrate the extended pelvis.20 We propose that a spinal osteotomy should be performed before THR. The purpose of this retrospective study was to review our experience in 28 consecutive patients with AS who underwent both spinal osteotomy and THR.

Patients and Methods From September 2004 to November 2012, 329 patients with AS underwent a spinal osteotomy in the spinal unit and 248 patients underwent a THR in joint unit of our institute. Of this cohort, 28 patients underwent both a spinal osteotomy and a THR and were reviewed in this study. We diagnosed AS according to the New York criteria.21 The chief complaint of most of patients was an inability to look straight ahead or to lie flat. The deformities had severely restricted their interpersonal THE BONE & JOINT JOURNAL

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communication and activities of daily living. Compression of the abdominal viscera leading to indigestion was common. In total, 22 patients had a spinal osteotomy before a THR (group 1), and six patients underwent a THR before spinal osteotomy (group 2). Pre- and post-operative full-length spinal radiographs of patients standing in a neutral unsupported position and including the whole spine and pelvis were performed on all patients. The type of osteotomy included pedicle subtraction osteotomy (PSO)11, vertebral column decancellation (VCD)22 and transpedicular bivertebrae wedge osteotomy and discectomy.23 We used a pulmonary hilum as the centre of gravity of the trunk to calculate the required degree of osteotomy by shifting the plumb line through pulmonary hilum to hip axis.24 The required angle for the spinal osteotomy was calculated based on the normal range of movement (ROM) of the hip joint. Unilateral THR was performed in only one patient and the other 27 patients had bilateral THRs. A pre-operative standing lateral view of the pelvis helped with the positioning of the patient on the operating table and a standard THR was performed. For all patients, a posterior or posterolateral approach was used. There was difficulty in visualising the femoral neck using the posterior approach particularly in patients with a pre-operative external rotation deformity of the hip. Identifying the neck required dissecting anterior to the greater trochanter and the abductor muscles. The exposure of the lesser trochanter of the femur when the posterolateral approach was used was beneficial if a femoral-neck osteotomy was needed. Thorough excision of the articular capsule and osteophytes facilitated exposure of the acetabulum. The acetabular preparation involved piecemeal removal of the remaining femoral-head. The ligamentum teres attaches to the femoral fovea and allows for location of the original joint plane. Trial reduction was performed after positioning of the trial components in order to check for stability in all directions. The components were then implanted, short external rotator muscles were repaired and the wound closed in layers over a drain. All patients were extubated immediately after the spinal osteotomy. Drains were removed when blood collection was less than 50 ml per 24 hours. Patients were typically allowed to mobilise within 48 to 72 hours using a thoracolumbosacral orthosis, which was worn for three months. If the THR was performed before spinal osteotomy, four pillows to support the patients’ upper back and neck were used, because of their spinal deformity (Fig. 1). Patients were allowed to walk with support after three weeks, and full weight-bearing was permitted after six weeks. Serial post-operative radiographs and clinical examination were conducted immediately after surgery, at six and 12 months post-operatively and at the time of the final follow-up. No patient was lost to follow-up. The kyphosis angles were measured on lateral radiographs in the

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standing position. The mean duration of follow-up was 3.5 years (2 to 9). Student's t-test was used for analysis, and statistical significance was measured at p < 0.05. Statistical analysis was performed using SPSS 14.0 for Windows (SPSS Inc, Chicago, Illinois).

Results The patients’ height increased from mean 129.4 cm (118 to 147) to 158.4 cm (153 to 168) (p < 0.001). The spinal sagittal Cobb angle of the vertebral osteotomy segment was corrected from an average pre-operative kyphosis 32.4º (-22° to -46°) to a post-operative lordosis 29.6° (24° to 34°) (p < 0.001). About 1 cm to 1.5 cm sagittal translation at the osteotomy site occurred in three patients during the correction (two patients in group 1 and one in group 2). Fusion of the osteotomy was achieved in all patients, and no loosening or breakage of pedicle screws occurred. Significant improvements in pain, function and ROM were observed following THR (Table I). The mean flexion ranges was 89. 2° (81° to 103°), and a mean extension was 17. 2° (13° to 21°). In group 2, two of six patients sustained an anterior dislocation in the early period (one after three days and the other after six days), and reduction was performed under general anaesthesia. A spinal osteotomy was then performed two weeks after the THR. The other four patients had a spinal osteotomy at three to six months after THR. At the last follow-up, heterotopic ossification was present in three of 56 hips and none required a surgical revision or re-operation in either of the two groups. Discussion We recommend that a spinal osteotomy should be performed before a THR for a number of reasons. Firstly, AS patients with a severe kyphosis deformity have the potential risk of dislocation of the prosthesis, especially in the early periods after the THR.19 Also, the required correction angle of spinal osteotomy can be calculated according to pelvic incidence (PI), an anatomical parameter of the pelvis24-26 and as a relatively normal alignment can be achieved between the spine and the pelvis after spinal osteotomy and this may help with the positioning of the acetabular component.19 Not least, if the spinal deformity was previously corrected, the pre-operative and post-operative management of THR can be performed more safely (Fig. 2). It is important to consider the spine and hip deformities as one entity rather than separately. It is known that over time, the kyphotic deformity resulting from AS may cause a downward and forward shift of patient’s centre of gravity and then the patient’s lower extremities compensate for the sagittal imbalance by extension of the hips, flexion of the knees, and plantar flexion of the ankles. If THR was performed before the spinal osteotomy and the ROM was restored, the hip joint may be excessively hyperextended once the patient resumes an upright position and which

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Fig. 1a

Fig. 1b

Fig. 1d

Fig. 1c

Figure 1a – pre-operative clinical photograph showing a 46-year-old man with complaints of pain in the back and hips. An AS-related kyphotic deformity restricted his psychosocial activities and physical functioning. A total hip replacement was performed before a spinal osteotomy owing to technical problems related to positioning of the patients on the operating table. Figure 1b – a CT reconstruction shows that the spine and hip were both involved. Figure 1c – post-operatively the patient still could not lie straight on the bed owing to the spinal deformity. Figure 1d – an anterior dislocation occurred at the third post-operative day. Figure 1e – a spinal osteotomy was performed two weeks after the total hip replacement. Fig. 1e

explains the risk of dislocation. Tang et al19 confirmed this using a stereolithographic model of a pelvis. The first report recommending that a THR be performed before a spinal osteotomy was in 1963.27 The reason given was that the improved ROM of the hip and overall pain relief gives a more accurate assessment of residual spinal deformity in patients with severe hip flexion deformity.28 However, in our view this is not so, as not all AS patients have a flexion hip deformity. Song24 and Van Royen23 developed a biomechanical and mathematical method for

measuring deformity during planning sagittal plane corrective osteotomies of the spine for AS. Van Royen also developed a computer-based program for analysis and visualising the planning procedure for sagittal plane correction.26 Our method was to calculate the ideal post-operative pelvic tilt (PT) individually according to pre-operative PI, an unchanged anatomical parameter and then define the post-operative plumbline through the hip axis.29 The required angle to shift the trunk’s centre of mass was the angle required for the spinal osteotomy.24 THE BONE & JOINT JOURNAL

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Table I. Patient data

Spinal osteotomy Mean (SD) Cobb angle (°) Mean (SD) height (cm) Mean (SD) Oswestry Disability Index Mean (SD) Scoliosis Research Society score Function Pain Appearance Mental Satisfaction THR Mean (SD) Harris hip score

Fig. 2a

Pre-operative (SD)

Post-operative (SD)

p-value

-32.4 (15.5) 129.4 (13.1) 2.0 (0.6)

29.6 (11.2) 158.4 (11.6) 0.4 (0.4)

< 0.001 < 0.001 < 0.001

2.4 (0.3) 2.3 (0.7) 1.6 (0.5) 2.2 (0.9) -

4.2 (0.4) 4.3 (0.4) 4.3 (0.4) 4.2 (0.6) 4.7 (0.3)

< 0.001 < 0.001 < 0.001 < 0.001 -

29.5 (4.3)

88.4 (5.2)

< 0.001

Fig. 2c

Fig. 2b

Fig. 2d

Fig. 2e

Figure 2a – photograph showing a 45-year-old man with ankylosing spondylitis before spinal osteotomy. Figure 2b and c – pre-operative radiographs show that the spine was involved. Figure 2d – post-operative radiograph shows good alignment of the spine. Figure 2e – photograph demonstrates that the patient could lie straight on the bed after the spinal osteotomy, and no obvious hip flexion deformity could be seen.

Conventionally, the main osteotomies for correcting fixed sagittal deformity were the Smith-Petersen osteotomy (SPO),30 and pedicle subtraction osteotomy (PSO).31-33 In a meta-analysis Van Royen et al34 found that the mean VOL. 96-B, No. 3, MARCH 2014

correction of patients with AS who underwent correction of fixed kyphotic thoracolumbar deformity was about 40.3° for opening wedge osteotomies and 36.5° for closing wedge osteotomies. They noted a tendency toward less severe

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complications, such as vascular complication, with the closing wedge osteotomy. More recently, Wang reported a more powerful osteotomy to correct severe spinal deformity, the VCD.22 Therefore, decision making for spinal osteotomy should be made according to what corrective angle the patient requires. For a THR, attention to detail is important because technical problems related to the position of patients on the operating table, as well as the accurate positioning of components in the presence of fixed pelvic obliquity or pelvic tilting, is difficult.35,36 Bhan et al35 found that exaggerated anteversion may lead to intra-operative difficulties including impingement of the prosthetic neck or the greater trochanter posteriorly or difficulties in the placement of the hip, reduction of the hip, or both, in addition to causing subsequently anterior instability. Tang et al19 postulated that this anatomical abnormality may lead to a more anteverted and vertical inclination of the acetabular cup. Pelvic hyperextension brings the cup to a more open position with an exaggerated anteversion. Therefore, it is important to assess the relationship of the pelvis to the lumbar spine in order to prevent future acetabular component malposition.19 Spinal complications such as intra-operative paraplegia can occur during THR. Danish et al37 described two patients with AS who underwent a THR and had intraoperative thoracic vertebral body extension fractures with resultant acute traumatic paraplegia, owing to the surgical positioning,37 although this injury usually occurred during hospital bed transfers and falls.38,39 The possible mechanism for this was hyperextension of immobile spine.40 The separate weight of the upper and lower body can act as lever arms on the cranial and caudal portions of the stiff spine.41 Shearing fractures occur most commonly through the intervertebral disc space, involving the posterior elements and less frequently, the vertebral body (VB).28,39,41 Rigidity, as well as the presence of osteoporosis of the spine increases the risk of vertebral body fracture and subsequent spinal cord injury.42 If the spinal deformity was previously corrected, the pre-operative and post-operative management of a THR should be able to be performed more conveniently and safely. In conclusion, we believe that a spinal osteotomy should be performed before a THR, unless the deformity is so severe that the intra-operative positioning cannot be undertaken. Professor Y. G. Zhang is equal first author of this article. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. This article was primary edited by S. Hughes and first-proof edited by D. Rowley.

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