Functional Leg-length Inequality Following Total Hip Arthroplasty

Transcription

1 The Journal of Arthroplasty Vol. 12 No Functional Leg-length Inequality Following Total Hip Arthroplasty Chitranjan S. Ranawat, MD, and Jos~ A. Rodriguez, MD Abstract: A consecutive series of 100 patients undergoing primary total hip arthroplasty were assessed for functional leg-length inequality (FLLI). In addition, the medical records of all patients treated for FLLI by the senior author (C.S.R.) in the past 15 years was reviewed. A questionnaire was distributed to the members of The Hip Society specifically to query the prevalence, etiology, and management of FLLI. Fourteen percent of patients were noted to have pelvic obliquity and FLLI 1 month after surgery. All had resolution of the symptoms by 6 months after surgery. Nine patients have been identified over the past 15 years with persistent FLLI. Among the causes suggested by respondents to the questionnaire are tightness of periarticular soft tissues with resultant pelvic obliquity and degenerative conditions of the spine with contracture. Methods of treatment and prevention are discussed. Key words: hip, prosthesis, leg length, pelvic obliquity. The sensation of limb-length inequality after total hip arthroplasty (THA) has been well described [1-4]. Most often this sensation relates to a change in the actual length of the reconstructed hip, sometimes requiring a contralateral shoe lift for correction. Techniques of accurate preoperative templating, anatomic component geometry, and intraoperative assessment have diminished the prevalence of inadvertent lengthening of the limb by reproducing the normal anatomic relationships {2,5-7]. A small number of patients, however, may suffer from a sense of functional limblength inequality despite attempts to accurately restore these anatomic relationships. When a sense of leg-length discrepancy occurs after THA, it can usually be broken down into two components [8]. The actual or true leg-length inequality is caused by lengthening of the prosthetic head-neck distance. The apparent or functional leg-length inequality (FLLI) describes the From the Center for Total Joint Replacement, Lenox Hill Hospital, New York, New York. Reprint requests: Chitranjan S. Ranawat, MD, Center for Total Joint Replacement, Lenox HilI Hospital, 130 East 77th Street, 1 lth Floor, New York, NY Churchill Livingstone Inc. amount that is attributable to other factors such as the tightness of the anterolateral soft tissues about the hip and degenerative disease with scoliosis of the lumbar spine, causing obliquity of the penis. The incidence and causes of functional leglength inequality are not well described. Most surgeons perform THA with the goal of reestablishing leg length, anatomic geometry equal to the normal opposite side, and optimal soft tissue tension around the hip to maximize stability. The soft tissue tension can be considered to have a horizontal component and a vertical component, both of which should be reestablished and balanced with hip arthroplasty. In cases where the horizontal component of the soft tissue tension is exceeded (offset increased), a painful stretching of the contracted anterior and lateral structures may result. Ireland and Kessel described the functional leglength inequality in children with pelvic obliquity [9]. Functional leg-length inequality after THA may similarly be caused by degenerative disease of the lumbar spine with structural scoliosis and pelvic tilt. In these cases, the limitation in the mobility of the spine makes patients more sensitive to alterations in the length and kinematics of the hip joint because of their inability to compensate for these changes. 359

2 360 The Journal of Arthroplasty Vol. 12 No. 4 June 1997 Pelvic obliquity may result from soft tissue tightness in the structures that cross the hip joint, joining the pelvis to the femur. These include the anterior capsule with the capsular insertion of the iliacus muscle, the rectus femofis musde and its origins, the psoas musde and tendon, the tensor fasda lata, the gluteus minimus muscle, and the gluteus medins muscle. Pelvic obliquity that results from abduction contracture of the hip will lead to a sense of lengthening on the affected side. Similar lengthening can occur with contralateral adduction contracture without soft tissue contracture on the affected side [9,10]. Preoperative flexion contracture similarly affects the lordotic position of the pelvis and lumbar spine. This may predispose to functional leg-length inequality if the anterior capsule remains tight after reconstruction, thereby limiting abduction and external rotation. Conversely, if the anterior capsule is appropriately released, and a flexion contracture persists in the contralateral hip, the pelvis is tilted to the contralateral side, resulting in a feeling of imbalance. The diagnosis of functional limb-length inequality is usually apparent when viewing the patient standing. The patients complain of a sense of imbalance and leg lengthening. Their pain may be in the groin or laterally in the abductor mechanism. Pain in the lower back or along the iliac crest may also be present. The knee is slightly flexed while the pelvis is tilted downward on the affected side as a result of the contracture of the lateral and or anterior structures. This position differs from that of an actual inequality where the pelvis is level or tilted away from the affected side. The patient's sensation of inequality will far exceed the radiographic measurements, and the gait appears awkward and painful. The FLLI is measured with the use of progressively thicker blocks under the contralateral foot until a sense of balance is felt by the patient. Examining the movement of the hip will reveal the abduction or abduction-flexion contracture. The patient is usually quite unhappy. We believe that in most of these patients, the FLLI has a self-limited course, whereas in a small number, the profound sense of inequality remains. In this study we sought to examine the incidence and natural history of FLLI and tried to identify predisposing factors and methods of treatment by reviewing our own cases as well as by polling the members of The Hip Society for their experience with this condition. Materials and Methods To document the incidence of FLLI, a consecutive series of IO0 patients undergoing primary THA by the senior author were retrospectively reviewed for the presence of pelvic obliquity and sensation of FLLI at the 1-, 3-, and 6-month follow-up visits. Anteroposterior radiographs of the pelvis were obtained using a standardized technique by the same technician. The presence of obliquity of the pelvis with respect to the spine and femurs was qualitatively noted. No measurement of angles was made. In addition, the range of motion was tested. When the patient had both radiographic evidence of pelvic tilt and tilt of the pelvic clinically as the leg approached neutral position (abduction contracture), the patient was designated as having a functional leg-length inequality. In addition, actual leg lengths were measured radiographically using the perpendicular distance connecting the line between the teardrops and the centerpoint of the lesser trochanters. The difference in leg lengths between the patients with and without pelvic obliquity was assessed using Student's t-test. Medical records were reviewed to identify predisposing clinical factors. In addition, the medical records of patients who have been treated by the senior author for persistent symptoms of FLLI within the past 15 years were reviewed. These data were collected by a single observer who was not the treating physician and in accordance with the guidelines of the Research and Clinical Investigations Committee at Lenox Hill Hospital. A questionnaire was distributed to the 90 members of The Hip Society to specifically query the prevalence, etiology, and management of FLLI (Table 1). More than 1 answer was frequently given to each of the questions, and all of the responses were summarized in tabular form (Table 2). Results Of 100 consecutive THAs performed at our center, 14 percent of cases were noted to have pelvic obliquity 1 month after surgery. These were usually hips with dysplasia and preoperative shortening (10 hips). All 14 of these patients had gradual resolution of the FLLI between 3 and 6 months after surgery with stretching exerdses. These can be considered transient functional leg-length inequalities (Fig. 1 ). Table 1. Hip Society Questionnaire 1. How many hip arthroplasties do you do a year? 2. Approximately how many patients have you seen with leglength inequality resulting from pelvic tilt in the postoperative period? 3. What do you believe are the causes for such leg-length inequality? 4. What forms of treatment, surgical or nonsurgical, have you used to rectify the pelvic tilt?

3 Table 2. Hip Society Survey Results (53 Respondents to 90 Questionnaires Sent) Functional Leg-length Inequality After THA Ranawat and Rodriguez Prevalence of functional leg-length inequality Transient with complete resolution Persistent 2. Proposed causes of pelvic obliquity and functional leg-length inequality Cause No. of Surgeons Responding % 0.5-7% Tight periarticular soft tissues 40 Abduction contractture 22 Preoperative shortening 5 Adduction contracture 3 Flexion contracture 2 Change in abductor mechanics 13 Trochanteric advancement 3 Increase in offset 6 Dysplasia, less valgus 4 Spine disease 2 i Spondylosis and stenosis 7 Scoliosis and structural obliquity 10 Iliolumbar contracture 4 Treatment No. of Surgeons Responding 3. Conservative treatment Time alone 11 Physical therapy 33 Lumbar mobility, "hula," or pelvic tilt 14 Abductor stretching 18 Extension exercises 2 Shoe lift Surgical treatments performed Soft tissue release 9 Psoas tendon 1 Tensor fascia lata 3 Adductor tendon 2 Abductor release (iliac crest) 1 Anterior capsule and minimus 2 Shortening of prosthetic component 6 The actual leg-length measurements demonstrated that the operated leg was lengthened by an average of 3.4 mm (range, 10 mm of shortening to 18 mm of lengthening with a SD of 3.6 mm). The leg was lengthened by 0-7 mm in 61% of cases. The actual leg-length discrepancy was between -4 and 10 mm in 94% of cases. There was no statistical difference in actual leg-length change between the group with pelvic obliquity (n = 14) and the group without it (n = 86). We have noted persistent functional leg-length inequality in approximately 1 in 300 THAs performed at our center. Nine patients have been Fig. 1. Anteroposterior views of the pelvis of a 70-yearold woman with dysplasia and arthrosis. (A) Before surgery, she had restricted motion and slight superior migration of the hip. (B) After surgery, she had radiographically equal leg lengths, but functional leg-length inequality of 8 mm based on pelvic tilt. This resolved completely after 5 months. identified in the last 15 years with persistent functional inequality (Table 3). Persistent functional leg-length inequality is noted following THA usually in women who are of short stature (< 5 ft 6 inches) who have a varus alignment of the femoral neck, with or without flexion contracture, and small bony dimensions, or have a protrusio deformity and flexion contracture with limited range of motion (Fig. 2). Of these 9 patients with persistent FLLI, 5 were treated with contralateral shoe lift, 2 received additional physical therapy, and 2 underwent soft tissue release (I with concomitant prosthetic shortening) prior to resolution of the sense of inequality (Table 3). To the 90 questionnaires that were sent to the members of The Hip Society, 53 members (59%) responded with detailed answers, and these are summarized in Table 2. The prevalence of functional leg-length inequality was quite variable and diminished greatly with time after operation. Pelvic obliquity that was defined as transient with complete resolution was noted in 15-60% of cases. Forty respondents attributed the condition to a

4 362 The Journal of Arthroplasty Vol. 12 No. 4 June 1997 Table 3. Demographic and Treatment Data for Patients With Persistent Leg-Length Inequality (> 6 Months) Anatomic Functional Age(y)/ Hip Spine Inequality Inequality Sex Pathology Pathology Height (mm) (mm) Treatment 51/F Prostrusio L5-S 1 spondylosis 5 ft 5 inches i 0 Varus Flexion contracture Abduction contracture 62/F Mild protrusio Mild degenerative 5 ft 4 inches 2 disc disease Restricted motion Flexion < 75 Preoperative abduction contracture and pelvic tilt 68/F Prostrusio Degenerative scoliosis 5 It 6 inches 6 Varus 50/M Contralateral ankylosis Lumbar spondylosis 5 ft 6 inches 8 45/F Protrusio LS-S1 spondylosis 5 ft 6 inches 4 Flexion contracture Adduction contracture 73/F Restricted motion Degenerative scoliosis 5 ft 4 inches 5 Flexion < 80 Preoperative pelvic tilt 66/M Restricted motion L5-S1 degenerative disc 5 ft 5 inches 11 Flexion < 60 57/F Protrusio L5-S1 spondylosis 5 ft 6 inches 6 67/F Flexion contracture Degenerative scoliosis 5 ft 4 inches 3 15 Shoe lift 12 Shoe lift Shoe lift Shoe lift Lift, physical therapy Physical therapy Physical therapy Soft tissue release Soft tissue release and prosthetic shortening tightness of the periarticular soft tissue structures that caused abduction and/or flexion contracture with pelvic tilt. Thirteen surgeons specifically mentioned the change in abductor mechanics with trochanteric advancement or a change in the offset of the hip as the cause of pelvic obliquity. Degenerative conditions of the spine with contracture were described by 21 surgeons as causative of this Condition. Persistent functional leg-length inequality was noted in 0.5-7% of cases. As treatment for functional leg-length inequality, 11 surgeons recommended observation until the contracture has time to work itself out. Thirty-two respondents recommended physical therapy to help improve the time to resolution, with pelvic tilt or "hula" exercises, as well as spedfic abductor stretching and exercises. A contralateral shoe lift was recommended by 14 surgeons until the sense of inequality resolves. Persistent functional leg-length inequality has been approached with surgery by 15 Fig. 2. Anteroposterior views of the pelvis of a 45-year-old woman with protrusio deformity with inflammatory arthritis associated with a varus femoral neck and a flexion contracture. (A) After surgery she had 4 mm of actual leg lengthening, but 14 mm of functional leg lengthening based on pelvic tilt. (B) With physical therapy this has improved partially after 8 months, and she uses a lift of 6 mm in the contralateral shoe.

5 Functional Leg-length Inequality AfterTHA Ranawat and Rodriguez 363 of the respondents. Nine surgeons have performed a soft tissue release, and 6 others have performed an exchange to a shortened prosthetic component. Discussion The concept of functional leg-length inequality is not well described. Our goals in this study were to present a group of patients whose sense of leglength inequality surpasses any actual difference in the leg lengths and to describe the natural history of this condition, noting possible predisposing factors and methods of treatment. Transient FLLI is sufficiently common that a random sample of 100 patients presented a cohort of 14 patients with FLLI. Persistent FLLI is rare and required a review of the last 15 years of THAs performed by the senior author to identify 9 cases. There may be additional cases of persistent FLLI who did not continue follow-up treatment at our institution. The canvassing of the members of The Hip Society for their experience with this condition is admittedly less precise than a consecutive series, but it allows the broader experience of surgeons with specific expertise in hip disease to be presented. Most patients with FLLI will have gradual improvement in their symptoms with appropriate physical therapy to help stretch the tight soft tissue structures and thereby relieve the pelvic obliquity (Abraham and Dimon, unpublished data, 1991). This type of transient FLLI commonly occurs in dysplastic hips with associated valgus and antetorsion. When the arthritis results in a flexion-abduction contracture, reconstruction with most standard implants will increase the offset of this typically valgus femoral neck (Fig. 1). A small increase in the actual length (ie, 5 mm) may produce a significant functional inequality if the soft tissue structures are left too tight. In these patients, the sensation of inequality usually resolves in ~the months following arthroplasty with appropriate physical therapy, as occurred in our cohort. The exercises that we advocate are stretching of the anterior structures by lying prone and hyperextension of the lumbar spine and hips by pushing the torso up on the arms. The affected leg can be safely crossed behind the other leg in this extended position with the pelvis held fixed, to further stretch the tight lateral structures of the hip. In addition, standard "pelvic tilt" exercises, bringing the affected hip into a neutral to slightly adducted position, will address the tight lateral structures. During this initial postoperative period, walking with pelvic obliquity and functional inequality may produce secondary symptoms in the adjoining joints. Low back and buttock pain may occur, particularly when lumbar facet arthrosis preexisted [11]. Patients who have valgus deformity and arthrosis of the ipsilateral knee may see an acute worsening of the lateral compartment or patellofemoral symptoms. Resolution of these symptoms will occur with improvement in the pelvic obliquity. Preexisting degenerative disease of the lumbosacral spine with scoliosis can further accentuate the pelvic tilt and FLLI. Lack of mobility in the lumbosacral spine can interfere with compensation, often results in back pain after surgery [ii], and predisposes to persistent FLLI. After 4-6 months of conservative treatment with physical therapy, one should be able to assess the progress or improvement in the pelvic obliquity. Those patients who do not achieve symptomatic improvement with physical therapy may benefit from surgical release of the tight soft tissue structures. During such an operation, attention should be paid to correct any anatomic inequality that exists. With an anatomic inequality of less than 5 mm, simple soft tissue release should be sufficient to improve symptoms. Infrequently, the offset of the femoral component may need to be diminished, by exchanging either a modular femoral head or a different femoral component. All structures about the hip, such as the anterior capsule, gluteus minimus, rectus femoris, and tensor fascia lata, should be tested for tightness and appropriately released. Two patients have undergone this type surgical release of the periarticular soft tissues with resolution of their symptoms, 1 with concomitant prosthetic shortening (Fig. 3). Technique for Prevention While performing a primary THA through a posterior exposure, the surgeon should seek to reproduce the normal anatomy in terms of neck length, offset, and socket position, while ensuring proper balance of the soft tissue envelope. A small increase in the neck length may help with stability; however, every attempt should be made not to increase the leg length by more than 1-10 mm. Once the reconstructed hip is reduced, the soft tissues should be routinely checked for tightness. The tensor fascia lata and rectus femoris muscles can be checked with the Ober test. The gluteus minimus can be directly palpated beneath the medius and released if necessary. The anterior capsule can be palpated with the hip in full extension and external rotation. If the capsule feels tight, like a cord, or if the hip will not externally rotate enough for the posterior trochanter to come within 1 finger-

6 364 The Journal of Arthroplasty Vol. 12 No. 4 June 1997 Fig. 3. (A) Anterposterior view of the pelvis of a 67-year-old woman with persistent functional leg-length inequality of 18 mm in the face of an actual leg-lenth inequality of 3 mm and pain-associated joint stiffness. (B) After circumferential release of the capsule and pericapsular scar tissue, she underwent prosthetic shortening of 5 mm using a custom femoral component. After surgery she had complete resolution of her pain and felt well balanced, although her anatomic measurement was 3-4 mm shorter on the previously lengthened side. breadth from the ischial tuberosity, then surgical release of the capsule is advisable. Conclusion Functional legqength inequality has been noted to be transient in nature in 14% of patients undergoing THA. This is most likely related to soft tissue tightness and pelvic tilt. In most of these patients, the condition will respond to soft tissue stretching with physical therapy, and time. Persistent FLLI is a rare condition that is usually seen in patients of short stature with varus deformity or protrusio and often associated degenerative disease of the spine. When not very painful, this condition will respond to a contralateral shoe lift. When pain is a significant component of the complaints, a soft tissue release may help address the functional aspect of any length inequality. References 1. Williamson JA, Reckling FW: Limb length discrepancy and related problems following total hip replacement. Clin Orthop 134:135, Love BRT, Wright K: Leg length discrepancy after total hip replacement. J Bone Joint Surg 65B:103, Turula KB, Freiberg O, Lindholm TS et ah Leg length inequality after total hip arthroplasty. Clin Orthop 202:163, Edeen J, Sharkey PF, Alexander H: Clinical significance of leg length inequality after total hip arthroplasty. Am J Orthop 24:347, McGee JMJ, Scott JHS: A simple method of obtaining equal leg length in total hip arthroplasty. Clin Orthop I94:269, Miiller ME: Mfiller straight stem total hip replacement system. Protek, Berne, i Woolsen ST, Harris WH: A method of intraoperative limb length measurement in total hip arthroplasty. Clin Orthop 195:207, Abraham WD, Dimon JH: Leg length discrepancy in total hip replacement. Orthop Clin North Am 23:201, Ireland J, Kessel L: Hip adduction/abduction deformity and apparent leg-length inequality. Clin Orthop 153:156, Wagner H" Pelvic tilt and leg length correction. Orthopfide 19:273, Friberg O: Clinical symptoms and biomechanics of lumbar spine and hip joint in leg length inequality. Spine 8:643, 1983