Special Focus Section
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Instability after Total Knee Arthroplasty David Clinton McNabb, MD1
Raymond H. Kim, MD1,2,4
1 Colorado Joint Replacement, Denver, Colorado 2 Department of Mechanical and Materials Engineering, University of
Denver, Denver, Colorado
Bryan D. Springer, MD3,4
Address for correspondence Raymond H. Kim, MD, Colorado Joint Replacement, Porter Adventist Hospital, 2535 S. Downing Street, Suite 100, Denver, CO 80210 (e-mail: [email protected]).
3 OrthoCarolina Hip and Knee Center, Charlotte, North Carolina 4 Department of Orthopaedic Surgery, Joan C. Edwards School of
Medicine, Marshall University, Huntington, West Virginia
Abstract
Keywords
► ► ► ►
knee arthroplasty instability revision
Total knee arthroplasty (TKA) has shown to portend good long-term survivorship and excellent patient satisfaction. There are various etiologies of failure of a TKA. Instability is a major cause of the need for revision. Often, increased constraint is needed to supplement or perform the function of incompetent ligament and soft tissue structures. Posterior cruciate retaining (PCR) TKA has the least constraint. Posterior cruciate substituting (PS) TKA increases sagittal constraint. Varus–valgus constraint (VVC) adds a marked increase in coronal stability. The ultimate in constraint in TKA is a linked hinged implant. In revision TKA, it is the surgeon’s responsibility to implant the prosthesis with the necessary constraint to impart adequate stability.
Total knee arthroplasty (TKA) is a procedure that has provided good and excellent results in greater than 92 to 97% of patients, which has been reported by multiple studies at 10 to 15 years follow-up. 1–4 A recent study showed 82.7% survivorship at 30-year follow-up. 5 Over the past two decades, there has been a significant increase in the number of primary and revision TKA operations performed in the United States. From 2005 to 2020 alone, the demand for primary TKA is projected to grow from 471,088 to 1.37 million (291% increase) and total knee revisions are projected to increase from 47,236 in 2005 to 127,510 in 2020 (270% increase). 6 Other estimates show these numbers to grow to 3.48 million and 268,200, respectively, by 2030. 7 With this expected exponential increase in primary and revision TKAs, it is imperative for the surgeon to have a systematic approach in evaluating and treating a failed TKA. Revision TKA is a complex procedure. The basic principles involved in revision TKA include joint line restoration, reconstruction of bone deficiencies, restoration of appropriate mechanical alignment, and the provision of adequate stability. Stability may be provided by native soft tissue structures or by the prosthetic constraint of the device implanted. Each level of prosthetic constraint has unique benefits, as well as potential disadvantages, and requires varying levels of com-
received August 29, 2014 accepted after revision October 23, 2014 published online December 17, 2014
petency of native anatomic structures. This review discusses the evaluation and treatment of an unstable TKA.
Diagnosis There are numerous modes of failure for TKA including infection, aseptic loosening, instability, stiffness, and polyethylene wear.8–11 To appropriately manage the failed TKA, it is imperative for the surgeon to determine the exact mode of failure.
History The history must include the reason for the initial arthroplasty and any previous surgeries or injuries to the knee. Infection must be ruled out in the evaluation of every patient with a painful TKA. Pain should be differentiated between pain with weight bearing and pain at rest. Weight-bearing pain is often related to loosening, malalignment, or instability, whereas pain at rest may be related to overstuffed flexion or extension gaps, soft tissue impingement, component malposition, and/or infection.12,13 Instability is a common cause of revision TKA. The source of the instability can be straightforward or multifactorial. Potential causes of instability can include the following: trauma, ligamentous compromise such as those with significant preoperative
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DOI http://dx.doi.org/ 10.1055/s-0034-1396080. ISSN 1538-8506.
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J Knee Surg 2015;28:97–104.
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deformity who required aggressive soft tissue releases, obese patients, inadequate balance of flexion and extension spaces at the time of surgery, malpositioning of the joint line, systemic connective tissue disorder, or patients with significant hip, foot, or ankle deformities.14–17 Symptomatic instability occurs in less than 1 to 2% of patients after primary TKA, but overall, it accounts for 7.5 to 20% of all total knee revisions, which follows infection and aseptic loosening in the prevalence.7–10 Symptomatic instability is most commonly experienced by patients during transfers and stair climbing. These patients typically present with pain, buckling, giving way, and progressive weight-bearing deformity. The timing of instability symptoms in relation to the index procedure, as well as any history of postoperative trauma to the knee may help determine the cause of instability.15–17 Patients who complain of instability in the immediate postoperative period most likely have asymmetric ligament balance, component malalignment, or may have suffered an iatrogenic ligamentous injury. A patient who originally had a stable primary TKA, but complains of late instability may have pseudolaxity because of asymmetric polyethylene wear or true laxity secondary to attrition of the collateral or posterior cruciate ligaments (PCL).
Physical Examination General examination of overall limb alignment and gait, as well as a focused examination of the knee is necessary. Initially, the skin should be inspected for any skin discoloration, prior surgical incisions, and any evidence of infection. Both passive and active range of motion should be assessed, as well as hamstring and quadriceps strength. The knee should be palpated to evaluate for synovial irritation that may be indicative of an oversized or overhanging component.18 Coronal and sagittal stability should be evaluated in full extension as well as at 30, 60, and 90 degrees of flexion.15,19 With the patient in supine position, evaluation of the anterior contour of the knee when placed at 90 degrees of flexion can be helpful in assessment of sagittal plane instability. If a posterior tibial subluxation is observed, called the “posterior sag sign,” PCL insufficiency in a cruciate-retaining knee is likely (►Fig. 1). Subtle midflexion instability is often best detected with the patient sitting with their legs hanging freely off of the exam table. The examiner then stabilizes the distal femur with one hand while varus and valgus torque are applied with the other hand. Flexion instability, as evidenced by the excessive anteroposterior movement and reproduction of symptoms during stress testing, often presents as chronic pes anserinus bursitis, not uncommonly in conjunction with distal iliotibial band tendinitis and tenderness around Gerdy tubercle.
suggestive of loosening. Component migration on successive radiographs is pathognomonic for loosening. It is important that the radiographs are obtained with the X-ray beam directed tangential to the fixation interface. As little as 6 degrees of angulation of the X-ray beam may obscure radiolucent lines.20 In addition to routine standard radiographs, numerous additional views may be of benefit in selected situations. A lateral radiograph with the limb in maximal flexion can assist in the diagnosis of sagittal plane instability.20–22 Varus–valgus stress radiographs in 30 degrees of flexion may detect subtle coronal plane instability. Comparison lateral radiographs of the contralateral native knee with magnification markers can aid in detecting an undersized femoral component, which often results in instability, or oversized femoral components, which may result in postoperative stiffness. PCL laxity may be detected by obtaining weight-bearing lateral views in both full extension and maximum flexion. Femoral–tibial contact in deep flexion that is positioned substantially more anterior than in full extension is consistent with PCL laxity. Occasionally, additional imaging modalities other than plain radiographs are necessary to make a diagnosis. Computerized tomography (CT) may be used to assess component rotation. Excessive internal or external rotation of the femoral component relative to the transepicondylar axis may lead to stiffness or instability.22,23 CT evaluation may also better assess osteolysis secondary to polyethylene wear. Bone scans, while nonspecific, can be helpful in the diagnosis of conditions such as prosthetic loosening, infection, or stress fracture.
Prosthetic Constraint Options While achieving a stable TKA, it is important to utilize the least amount of prosthetic constraint that is necessary to gain stability as implant durability is inversely proportional to the level of prosthetic constraint.24 However, in the revision TKA setting, native anatomic structures are often compromised and unable to provide adequate stability such that the use of increased prosthetic constraint is often required to achieve adequate stability. The levels of increasing prosthetic
Radiographic Evaluation Conventional radiographs are the initial imaging modality in the evaluation of the symptomatic TKA. Long leg alignment films, as well as routine weight-bearing anteroposterior and lateral views of the knee should be obtained in full extension. Radiolucent lines greater than 2 mm in multiple zones are The Journal of Knee Surgery
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Fig. 1 Knee with a posterior cruciate retaining total knee arthroplasty demonstrating a posterior sag due to posterior tibial subluxation, as a result of posterior cruciate ligament attenuation or unrecognized insufficiency at the index procedure.
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Posterior Cruciate Ligament Retention The least constrained total knee designs utilized in revision TKA are the posterior cruciate retaining (PCR) implants. They offer the advantages of minimized bone resection and may improve proprioception secondary to the retention of neural mechanoreceptors within the PCL, although this benefit remains controversial. However, standard PCR designs provide minimal intrinsic stability and are reliant on high-quality bone with intact collateral ligament structures. In addition, an intact functional PCL is essential. For these reasons, in the revision TKA setting, PCR designs are infrequently an acceptable option to provide adequate stability. In the presence of significant flexion instability, or an attenuated/nonfunctional PCL, revision with a PCR design is most likely to fail.25–27 Pagnano et al reported a series of 25 cases of flexion instability in PCR TKA treated with either isolated polyethylene exchange or conversion to a PS TKA design. In their series, 86% of 22 knees converted to PS TKA designs had marked pain relief and only one had recurrent instability. In contrast, two of three patients in that series treated with isolated polyethylene-bearing exchange suffered recurrent instability and required conversion to a PS TKA.25 In another report, six patients treated with conversion to PS designs had resolution of their instability, whereas both the patients treated with implantation of a more conforming PCR insert complained of recurrent instability.26 On the basis of these studies, if incompetent ligaments were identified, revision to more highly constrained components was recommended. Recently, there have been polyethylene designs within the PCR knee portfolio of some companies labeled ultracongruent. These more constrained polyethylene inserts have an additional buildup anteriorly and a more conforming surface to serve as the physical stop for posterior translation of the tibia. This design has shown success in revising PCR knees for PCL attenuation or incompetence. Hofmann et al reported on 47 patients revised from standard PCR inserts to ultracongruent inserts, only two of the knees had to be revised and neither were due to anterior– posterior instability.28 Berend et al demonstrated excellent outcomes in 97% of 312 primary TKAs in patients with PCL incompetency treated with ultracongruent polyethylene inserts.29 In addition, when comparing 121 PS primary TKA to 88 ultracongruent PCR primary TKA, Parsley et al found no significant difference in range of motion, Knee Society knee scores and functional scores.30 Provided component positioning is appropriate, extrapolating the data from the three earlier mentioned studies revising a PCR knee arthroplasty that has developed PCL incompetency to an ultracongruent liner may be a viable option.
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Posterior Cruciate Ligament Substitution (Posterior Stabilized) PS TKA designs offer greater anterior–posterior translational stability compared with standard PCR designs, but provide minimal increase in VVC or rotational constraint. The spinecam mechanism allows for more normal posterior femoral rollback and eliminates the technical aspects of balancing the PCL. As with PCR designs, intact medial and lateral collateral ligament complexes are mandatory when a PS design is selected in revision TKA secondary to the relatively short post-height and laxity of coronal fit within the intercondylar box of the femoral component.24,31 Obtaining a well-balanced flexion–extension gap is imperative when implanting a PS TKA to prevent dislocation in knee flexion.14,27 Numerous authors have described excellent results using PS designs in revision cases in patients with intact collateral ligaments. Mabry et al reported greater than 90% survivorship at 10 years following the 29 revisions with PS designs.32 Schwab et al were able to utilize PS designs in 7 of 10 patients revised for flexion instability in primary posterior stabilized knee replacements without further instability.33 Despite these excellent results, one study found that 3 of 11 patients (27.3%) revised with PS designs required re-revision versus only 1 of 53 patients (1.9%) in which a VVC design was used. The high re-revision rate may be because of the fact that numerous patients had significant bone loss and osteolysis and likely had some degree of collateral ligamentous compromise at the index revision.34 On the basis of these studies’ findings, it is essential to have intact collateral ligaments, adequate bone stock, and appropriate soft tissue balancing when utilizing PS TKA designs in revision TKA. Therefore, if there is insufficiency of either collateral ligament complex, a more constrained prosthesis design is likely required.35
Varus–Valgus Unlinked Constrained Total Knee Arthroplasty The unlinked VVC design is next in the continuum of increasing constraint. The taller spine and tighter coronal fit within the intercondylar box provide enhanced varus–valgus stability. This post design feature imparts stability by limiting rotation, medial–lateral translation, and varus–valgus angulation (►Fig. 2A–C). In the presence of a completely incompetent medial collateral ligament, excessive stresses encountered by the spine-cam mechanism could lead to the ultimate failure of a VVC implant. The taller and more conforming spine-cam mechanism in VVC implants results in increased stress at both the fixation interface and constraining mechanism of the implant which may lead to early implant loosening or implant failure due to wear of the stabilizing spine. As a result of the increase constraint, stems should be considered for supplemental fixation due to increased forces across the bone–cement interface. Promising results with various VVC designs in the revision TKA have been reported by several authors. A recent study of 114 revision knee replacements with VVC design, showed 96% survivorship at 10 years.36 Similar results with success rates of 70 to 94% have been reported in series from other authors.37–44 In several of these studies, primary and revision The Journal of Knee Surgery
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constraint available in TKA designs are as follows: (1) PCL retaining ; (2) posterior cruciate substitution (PS); (3) varus– valgus constrained, sometimes referred to as semiconstrained or unlinked constrained designs; and (4) hinged or linked constrained designs. The revision prosthesis selected should provide the degree of stability necessary to correct the anticipated instability.
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Fig. 2 (A) Radiographs of a 48-year-old male patient who presented many years after an anterior cruciate ligament reconstruction. (B) A posterior cruciate substituting total knee arthroplasty (TKA) was performed, but soft tissues were poorly balanced. (C) The patient was revised to a varus– valgus constraint TKA and provided excellent medial/lateral stability.
cases were included and, as expected, a trend toward better results in the primary TKA setting was noted. Early results with modern implant designs have not validated the concern regarding the potential disadvantage of increased stress across the bone–implant interface leading to early loosening with the more constrained TKA designs. In the series by Rosenberg et al, only one of 33 patients required rerevision with follow-up ranging from 24 to 84 months although radiolucent lines up to 2 mm were present in nearly 60% of the patients.40 In a series by Nazarian et al reporting on 207 revisions with a follow-up duration ranging from 2 to 6 years, only four femoral components and six tibial components required re-revision.42 Wilike et al reported on 10-year follow-up of 234 VVC TKA revisions performed for soft tissue deficiency. At 10 years, they report 81% survivorship.43 Longer follow-up evaluation of these designs is needed to more clearly understand their long-term durability. Recently, rotating platform (mobile-bearing) unlinked VVC TKA designs have been introduced which offer the potential advantage of decreasing stress at both the spine-cam mechanism as well as the fixation interface.44–46 While fluoroscopic evaluation of axial rotation has shown reduced axial rotation following TKA, it has revealed that there are many in vivo outliers who demonstrate axial rotation magnitudes that exceed the rotational limits of most fixed-bearing designs.47 Jones et al demonstrated that the incorporation of polyethylene-bearing mobility minimizes the transfer of torsional The Journal of Knee Surgery
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stresses to the fixation interface that has been associated with failure of fixed-bearing TKA implants.48 Bearing mobility also reduces rotational stresses on constraining spines, potentially reducing spine wear. In vivo kinematic studies have demonstrated that a rotating platform bearing primarily tracts with the femoral component during axial rotation.49 This allows the constraining spine to remain self-centered within the intercondylar box, reducing rotational stress on the spine. Retrieval studies in failed fixed-bearing TKAs have demonstrated substantial postwear can occur.50 The wear pattern was often rotational and was particularly evident in TKAs with increased constraint, which can be lessened with a mobile-bearing rotating platform. Mobile-bearing designs, however, do add an additional wear interface and with inexperience or in the case of severe instability can add to the complexity of establishing a stable knee.
Linked Hinge Constrained Total Knee Arthroplasty The linked hinge TKA offers the greatest constraint of all implant designs currently used in revision TKA. VVC designs have been very effective in most cases of revision for substantial instability or bone loss. However, in the extreme cases of global instability (severe flexion instability with a massive flexion gap dimension), total loss of collateral ligamentous support, massive bone loss such that collateral ligament attachments have been lost, and in situations with severe posterior capsular insufficiency with uncontrolled
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Fig. 3 (A) Anteroposterior and lateral radiographs of a patient who had a dislocation with a poorly balanced posterior cruciate substituting total knee arthroplasty (TKA). (B) The patient was revised to a larger polyethylene insert that did provided stability. (C) Unfortunately, the patient developed an infection and had significant bone loss on explant. The patient was revised to a linked hinged constrained TKA after clearing the infection.
hyperextension increased constraint using a linked hinge design is indicated. Cases with massive osteolysis, particularly of the distal femur, often lose collateral ligamentous integrity due to loss of the osseous ligament attachments (►Fig. 3A–C). Uncontrolled hyperextension is most commonly observed in patients with paralytic conditions with marked quadriceps weakness in which the patient repeatedly hyperextends the knee to stabilize the limb during the stance phase of gait. Similar to VVC implants, rotating platform linked hinge devices are preferred to fixed bearing designs due to the lower stresses incurred by the implant and fixation interfaces secondary to the presence of bearing mobility. Another subset of patients that benefit from the increased constraint provided by a distal femoral replacing linked hinge device is elderly patients with osteoporosis and severely comminuted supracondylar femoral fractures.51–54 In a study by Berend and Lombardi, 39 patients were reviewed who were treated with a rotating hinge distal femoral replacement; 13 for periprosthetic fractures, one for a distal femoral nonunion, and one for an acute distal femur fracture. They observed an 87% survivorship at 46 months in this series.53 Despite the improved stability provided, linked hinge TKA devices (particularly fixed hinge implants) have a poor historical track record with high rates of loosening, recurrent instability, prosthetic failure, extensor lag, chronic pain, and infection.55–57 Springer et al noted a significant risk of complications including infection, patellar complications, and implant breakage and recommended the utiliza-
tion of distal femoral replacing linked hinge devices with caution.52 Hui and Fitzgerald reported a 23% incidence of major complications, primarily infection and loosening, in their series of 67 fixed hinged arthroplasties.55 In a series by Jones et al reporting on 1 to 3 year results of 108 GUEPAR fixed hinged total knees, 29% of patients had poor results. Prosthetic loosening occurred in 27% of patients, infection in 11%, and 50% patients had patellar complications.56 Other studies have also noted high rates of patellar complications, infection, and even periprosthetic fracture in linked–hinged fixed-bearing TKA.57,58 Results with newer hinge TKA designs which incorporate bearing mobility have shown more promising outcomes.59–63 It is difficult to determine, however, whether improved implant design or better patient selection has led to improved outcomes. Barrack et al reported on 16 salvage revisions with a second generation rotating hinge TKA and compared those to 87 less complicated revision procedures with a VVC design. There were similar outcomes when compared with the less constrained group with no evidence of loosening at 2 to 6 years.59 The series was expanded to 23 patients with 2- to 9-year follow-up and continued to show no evidence of early loosening.60 Barrack’s initial series was further expanded to 30 patients by Jones et al and showed 100% survivorship at 24 to 74 months follow-up.61 Loosening was not present in any patient. In a series of 72 salvage revision TKA procedures with a rotating hinge prosthesis reported by Deehan et al with an average follow-up of 10 years (range, 3–18 years), survival analysis showed 90% implant survival at 10 years and only The Journal of Knee Surgery
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one patient had evidence of aseptic loosening.62 Despite excellent long-term survivorship in this series, 15% of patients complained of a persistent dull ache and 7% have an extensor lag of greater than 5 degrees. It is important to note that even the minor elevation of the joint line in a hinged component can lead to significant loss of mechanical advantage for the quadriceps and should be avoided, as it exacerbates anterior knee pain, extensor lag, knee “buckling,” and actually produces a sense of instability in some patients. One of the benefits of this implant is that balancing the flexion and extension gaps is not required, making joint line restoration somewhat easier. Another series of 24 patients treated with rotating hinge prosthesis showed no evidence of loosening or mechanical failure at a follow-up of 21 to 62 months with a significant improvement in Knee Society scores postoperatively.63 Failure of a rotating hinged prosthesis leaves few reconstructive options. Reimplantation of a modular tumor prosthesis, allograft-prosthesis composite, above-the-knee amputation, and fusion become the remaining options. Therefore, these prostheses should be used only in the elderly low-demand patient population with a limited life expectancy or in extreme cases of instability.
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Summary Similar to the goals of primary TKA, revision TKA seeks to restore the function of the knee. Surgeons performing revision TKA must respect the complexity of the procedure and must have a methodical, stepwise approach in the management of the failed TKA. A thorough preoperative history and physical examination are the first step in determining the cause of failure and prevention of complications. Careful assessment of ligament integrity and range of motion, a clear interpretation of imaging modalities, and evaluation to rule out infection must be undertaken. Performing revision surgery without a clear cause of failure is not recommended and often leads to poor results. After determining the cause of failure, careful preoperative planning and meticulous surgical technique is essential to assure an optimal surgical outcome. In revision TKA performed for instability, prosthetic constraint should be titrated according to the deficiencies of the soft tissues after making every attempt to balance the soft tissues to achieve symmetrical flexion and extension gaps. As a general rule, the least amount of constraint necessary to provide adequate stability should be utilized. For this reason, PS TKA devices will provide adequate stability in a majority of cases, as most patients retain the integrity of the collateral ligaments in a revision setting. However, in cases with substantial collateral ligament laxity or severe flexion–extension gap mismatch, a VVC device is recommended. Revision TKA cases with completely incompetent collateral ligaments are a contraindication to use of a VVC device because of the excessive stresses incurred by the stabilizing spine, which will ultimately result in premature implant failure. In these extreme cases, a rotating platform-linked hinge prosthesis will likely be necessary to provide stability. The Journal of Knee Surgery
In cases with massive bone loss, global instability with uncontrolled hyperextension, or comminuted and osteopenic supracondylar periprosthetic fractures, a linked hinge prostheses is similarly indicated.
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Total Condylar III and Constrained Condylar total knee arthroplasty. J Arthroplasty 1996;11(8):916–922 Nazarian DG, Mehta S, Booth RE Jr. A comparison of stemmed and unstemmed components in revision knee arthroplasty. Clin Orthop Relat Res 2002;(404):256–262 Wilke BK, Wagner ER, Trousdale RT. Long-term survival of semiconstrained total knee arthroplasty for revision surgery. J Arthroplasty 2014;29(5):1005–1008 Bottlang M, Erne OK, Lacatusu E, Sommers MB, Kessler O. A mobile-bearing knee prosthesis can reduce strain at the proximal tibia. Clin Orthop Relat Res 2006;447:105–111 Nakayama K, Matsuda S, Miura H, Iwamoto Y, Higaki H, Otsuka K. Contact stress at the post-cam mechanism in posterior-stabilised total knee arthroplasty. J Bone Joint Surg Br 2005;87(4):483–488 Zingde SM, Leszko F, Sharma A, Mahfouz MR, Komistek RD, Dennis DA. In vivo determination of cam-post engagement in fixed and mobile-bearing TKA. Clin Orthop Relat Res 2014; 472(1):254–262 Dennis DA, Komistek RD, Mahfouz MR, Walker SA, Tucker A. A multicenter analysis of axial femorotibial rotation after total knee arthroplasty. Clin Orthop Relat Res 2004;(428):180–189 Jones VC, Barton DC, Fitzpatrick DP, Auger DD, Stone MH, Fisher J. An experimental model of tibial counterface polyethylene wear in mobile bearing knees: the influence of design and kinematics. Biomed Mater Eng 1999;9(3):189–196 Dennis DA, Komistek RD, Mahfouz MR, Outten JT, Sharma A. Mobile-bearing total knee arthroplasty: do the polyethylene bearings rotate? Clin Orthop Relat Res 2005;440:88–95 Puloski SK, McCalden RW, MacDonald SJ, Rorabeck CH, Bourne RB. Tibial post wear in posterior stabilized total knee arthroplasty. An unrecognized source of polyethylene debris. J Bone Joint Surg Am 2001;83-A(3):390–397 Davila J, Malkani A, Paiso JM. Supracondylar distal femoral nonunions treated with a megaprosthesis in elderly patients: a report of two cases. J Orthop Trauma 2001;15(8):574–578 Springer BD, Sim FH, Hanssen AD, Lewallen DG. The modular segmental kinematic rotating hinge for nonneoplastic limb salvage. Clin Orthop Relat Res 2004;(421):181–187 Berend KR, Lombardi AV Jr. Distal femoral replacement in nontumor cases with severe bone loss and instability. Clin Orthop Relat Res 2009;467(2):485–492 Appleton P, Moran M, Houshian S, Robinson CM. Distal femoral fractures treated by hinged total knee replacement in elderly patients. J Bone Joint Surg Br 2006;88(8):1065–1070 Hui FC, Fitzgerald RH Jr. Hinged total knee arthroplasty. J Bone Joint Surg Am 1980;62(4):513–519 Jones EC, Insall JN, Inglis AE, Ranawat CS. GUEPAR knee arthroplasty results and late complications. Clin Orthop Relat Res 1979; (140):145–152 Rand JA, Chao EY, Stauffer RN. Kinematic rotating-hinge total knee arthroplasty. J Bone Joint Surg Am 1987;69(4):489–497 Inglis AE, Walker PS. Revision of failed knee replacements using fixed-axis hinges. J Bone Joint Surg Br 1991;73(5):757–761 Barrack RL, Lyons TR, Ingraham RQ, Johnson JC. The use of a modular rotating hinge component in salvage revision total knee arthroplasty. J Arthroplasty 2000;15(7):858–866 Barrack RL. Evolution of the rotating hinge for complex total knee arthroplasty. Clin Orthop Relat Res 2001;(392):292–299 Jones RE, Barrack RL, Skedros J. Modular, mobile-bearing hinge total knee arthroplasty. Clin Orthop Relat Res 2001;(392): 306–314 Deehan DJ, Murray J, Birdsall PD, Holland JP, Pinder IM. The role of the rotating hinge prosthesis in the salvage arthroplasty setting. J Arthroplasty 2008;23(5):683–688 Westrich GH, Mollano AV, Sculco TP, Buly RL, Laskin RS, Windsor R. Rotating hinge total knee arthroplasty in severly affected knees. Clin Orthop Relat Res 2000;(379):195–208
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Instability after Total Knee Arthroplasty David Clinton McNabb, MD1
Raymond H. Kim, MD1,2,4
1 Colorado Joint Replacement, Denver, Colorado 2 Department of Mechanical and Materials Engineering, University of
Denver, Denver, Colorado
Bryan D. Springer, MD3,4
Address for correspondence Raymond H. Kim, MD, Colorado Joint Replacement, Porter Adventist Hospital, 2535 S. Downing Street, Suite 100, Denver, CO 80210 (e-mail: [email protected]).
3 OrthoCarolina Hip and Knee Center, Charlotte, North Carolina 4 Department of Orthopaedic Surgery, Joan C. Edwards School of
Medicine, Marshall University, Huntington, West Virginia
Abstract
Keywords
► ► ► ►
knee arthroplasty instability revision
Total knee arthroplasty (TKA) has shown to portend good long-term survivorship and excellent patient satisfaction. There are various etiologies of failure of a TKA. Instability is a major cause of the need for revision. Often, increased constraint is needed to supplement or perform the function of incompetent ligament and soft tissue structures. Posterior cruciate retaining (PCR) TKA has the least constraint. Posterior cruciate substituting (PS) TKA increases sagittal constraint. Varus–valgus constraint (VVC) adds a marked increase in coronal stability. The ultimate in constraint in TKA is a linked hinged implant. In revision TKA, it is the surgeon’s responsibility to implant the prosthesis with the necessary constraint to impart adequate stability.
Total knee arthroplasty (TKA) is a procedure that has provided good and excellent results in greater than 92 to 97% of patients, which has been reported by multiple studies at 10 to 15 years follow-up. 1–4 A recent study showed 82.7% survivorship at 30-year follow-up. 5 Over the past two decades, there has been a significant increase in the number of primary and revision TKA operations performed in the United States. From 2005 to 2020 alone, the demand for primary TKA is projected to grow from 471,088 to 1.37 million (291% increase) and total knee revisions are projected to increase from 47,236 in 2005 to 127,510 in 2020 (270% increase). 6 Other estimates show these numbers to grow to 3.48 million and 268,200, respectively, by 2030. 7 With this expected exponential increase in primary and revision TKAs, it is imperative for the surgeon to have a systematic approach in evaluating and treating a failed TKA. Revision TKA is a complex procedure. The basic principles involved in revision TKA include joint line restoration, reconstruction of bone deficiencies, restoration of appropriate mechanical alignment, and the provision of adequate stability. Stability may be provided by native soft tissue structures or by the prosthetic constraint of the device implanted. Each level of prosthetic constraint has unique benefits, as well as potential disadvantages, and requires varying levels of com-
received August 29, 2014 accepted after revision October 23, 2014 published online December 17, 2014
petency of native anatomic structures. This review discusses the evaluation and treatment of an unstable TKA.
Diagnosis There are numerous modes of failure for TKA including infection, aseptic loosening, instability, stiffness, and polyethylene wear.8–11 To appropriately manage the failed TKA, it is imperative for the surgeon to determine the exact mode of failure.
History The history must include the reason for the initial arthroplasty and any previous surgeries or injuries to the knee. Infection must be ruled out in the evaluation of every patient with a painful TKA. Pain should be differentiated between pain with weight bearing and pain at rest. Weight-bearing pain is often related to loosening, malalignment, or instability, whereas pain at rest may be related to overstuffed flexion or extension gaps, soft tissue impingement, component malposition, and/or infection.12,13 Instability is a common cause of revision TKA. The source of the instability can be straightforward or multifactorial. Potential causes of instability can include the following: trauma, ligamentous compromise such as those with significant preoperative
Copyright © 2015 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.
DOI http://dx.doi.org/ 10.1055/s-0034-1396080. ISSN 1538-8506.
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J Knee Surg 2015;28:97–104.
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deformity who required aggressive soft tissue releases, obese patients, inadequate balance of flexion and extension spaces at the time of surgery, malpositioning of the joint line, systemic connective tissue disorder, or patients with significant hip, foot, or ankle deformities.14–17 Symptomatic instability occurs in less than 1 to 2% of patients after primary TKA, but overall, it accounts for 7.5 to 20% of all total knee revisions, which follows infection and aseptic loosening in the prevalence.7–10 Symptomatic instability is most commonly experienced by patients during transfers and stair climbing. These patients typically present with pain, buckling, giving way, and progressive weight-bearing deformity. The timing of instability symptoms in relation to the index procedure, as well as any history of postoperative trauma to the knee may help determine the cause of instability.15–17 Patients who complain of instability in the immediate postoperative period most likely have asymmetric ligament balance, component malalignment, or may have suffered an iatrogenic ligamentous injury. A patient who originally had a stable primary TKA, but complains of late instability may have pseudolaxity because of asymmetric polyethylene wear or true laxity secondary to attrition of the collateral or posterior cruciate ligaments (PCL).
Physical Examination General examination of overall limb alignment and gait, as well as a focused examination of the knee is necessary. Initially, the skin should be inspected for any skin discoloration, prior surgical incisions, and any evidence of infection. Both passive and active range of motion should be assessed, as well as hamstring and quadriceps strength. The knee should be palpated to evaluate for synovial irritation that may be indicative of an oversized or overhanging component.18 Coronal and sagittal stability should be evaluated in full extension as well as at 30, 60, and 90 degrees of flexion.15,19 With the patient in supine position, evaluation of the anterior contour of the knee when placed at 90 degrees of flexion can be helpful in assessment of sagittal plane instability. If a posterior tibial subluxation is observed, called the “posterior sag sign,” PCL insufficiency in a cruciate-retaining knee is likely (►Fig. 1). Subtle midflexion instability is often best detected with the patient sitting with their legs hanging freely off of the exam table. The examiner then stabilizes the distal femur with one hand while varus and valgus torque are applied with the other hand. Flexion instability, as evidenced by the excessive anteroposterior movement and reproduction of symptoms during stress testing, often presents as chronic pes anserinus bursitis, not uncommonly in conjunction with distal iliotibial band tendinitis and tenderness around Gerdy tubercle.
suggestive of loosening. Component migration on successive radiographs is pathognomonic for loosening. It is important that the radiographs are obtained with the X-ray beam directed tangential to the fixation interface. As little as 6 degrees of angulation of the X-ray beam may obscure radiolucent lines.20 In addition to routine standard radiographs, numerous additional views may be of benefit in selected situations. A lateral radiograph with the limb in maximal flexion can assist in the diagnosis of sagittal plane instability.20–22 Varus–valgus stress radiographs in 30 degrees of flexion may detect subtle coronal plane instability. Comparison lateral radiographs of the contralateral native knee with magnification markers can aid in detecting an undersized femoral component, which often results in instability, or oversized femoral components, which may result in postoperative stiffness. PCL laxity may be detected by obtaining weight-bearing lateral views in both full extension and maximum flexion. Femoral–tibial contact in deep flexion that is positioned substantially more anterior than in full extension is consistent with PCL laxity. Occasionally, additional imaging modalities other than plain radiographs are necessary to make a diagnosis. Computerized tomography (CT) may be used to assess component rotation. Excessive internal or external rotation of the femoral component relative to the transepicondylar axis may lead to stiffness or instability.22,23 CT evaluation may also better assess osteolysis secondary to polyethylene wear. Bone scans, while nonspecific, can be helpful in the diagnosis of conditions such as prosthetic loosening, infection, or stress fracture.
Prosthetic Constraint Options While achieving a stable TKA, it is important to utilize the least amount of prosthetic constraint that is necessary to gain stability as implant durability is inversely proportional to the level of prosthetic constraint.24 However, in the revision TKA setting, native anatomic structures are often compromised and unable to provide adequate stability such that the use of increased prosthetic constraint is often required to achieve adequate stability. The levels of increasing prosthetic
Radiographic Evaluation Conventional radiographs are the initial imaging modality in the evaluation of the symptomatic TKA. Long leg alignment films, as well as routine weight-bearing anteroposterior and lateral views of the knee should be obtained in full extension. Radiolucent lines greater than 2 mm in multiple zones are The Journal of Knee Surgery
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Fig. 1 Knee with a posterior cruciate retaining total knee arthroplasty demonstrating a posterior sag due to posterior tibial subluxation, as a result of posterior cruciate ligament attenuation or unrecognized insufficiency at the index procedure.
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Posterior Cruciate Ligament Retention The least constrained total knee designs utilized in revision TKA are the posterior cruciate retaining (PCR) implants. They offer the advantages of minimized bone resection and may improve proprioception secondary to the retention of neural mechanoreceptors within the PCL, although this benefit remains controversial. However, standard PCR designs provide minimal intrinsic stability and are reliant on high-quality bone with intact collateral ligament structures. In addition, an intact functional PCL is essential. For these reasons, in the revision TKA setting, PCR designs are infrequently an acceptable option to provide adequate stability. In the presence of significant flexion instability, or an attenuated/nonfunctional PCL, revision with a PCR design is most likely to fail.25–27 Pagnano et al reported a series of 25 cases of flexion instability in PCR TKA treated with either isolated polyethylene exchange or conversion to a PS TKA design. In their series, 86% of 22 knees converted to PS TKA designs had marked pain relief and only one had recurrent instability. In contrast, two of three patients in that series treated with isolated polyethylene-bearing exchange suffered recurrent instability and required conversion to a PS TKA.25 In another report, six patients treated with conversion to PS designs had resolution of their instability, whereas both the patients treated with implantation of a more conforming PCR insert complained of recurrent instability.26 On the basis of these studies, if incompetent ligaments were identified, revision to more highly constrained components was recommended. Recently, there have been polyethylene designs within the PCR knee portfolio of some companies labeled ultracongruent. These more constrained polyethylene inserts have an additional buildup anteriorly and a more conforming surface to serve as the physical stop for posterior translation of the tibia. This design has shown success in revising PCR knees for PCL attenuation or incompetence. Hofmann et al reported on 47 patients revised from standard PCR inserts to ultracongruent inserts, only two of the knees had to be revised and neither were due to anterior– posterior instability.28 Berend et al demonstrated excellent outcomes in 97% of 312 primary TKAs in patients with PCL incompetency treated with ultracongruent polyethylene inserts.29 In addition, when comparing 121 PS primary TKA to 88 ultracongruent PCR primary TKA, Parsley et al found no significant difference in range of motion, Knee Society knee scores and functional scores.30 Provided component positioning is appropriate, extrapolating the data from the three earlier mentioned studies revising a PCR knee arthroplasty that has developed PCL incompetency to an ultracongruent liner may be a viable option.
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Posterior Cruciate Ligament Substitution (Posterior Stabilized) PS TKA designs offer greater anterior–posterior translational stability compared with standard PCR designs, but provide minimal increase in VVC or rotational constraint. The spinecam mechanism allows for more normal posterior femoral rollback and eliminates the technical aspects of balancing the PCL. As with PCR designs, intact medial and lateral collateral ligament complexes are mandatory when a PS design is selected in revision TKA secondary to the relatively short post-height and laxity of coronal fit within the intercondylar box of the femoral component.24,31 Obtaining a well-balanced flexion–extension gap is imperative when implanting a PS TKA to prevent dislocation in knee flexion.14,27 Numerous authors have described excellent results using PS designs in revision cases in patients with intact collateral ligaments. Mabry et al reported greater than 90% survivorship at 10 years following the 29 revisions with PS designs.32 Schwab et al were able to utilize PS designs in 7 of 10 patients revised for flexion instability in primary posterior stabilized knee replacements without further instability.33 Despite these excellent results, one study found that 3 of 11 patients (27.3%) revised with PS designs required re-revision versus only 1 of 53 patients (1.9%) in which a VVC design was used. The high re-revision rate may be because of the fact that numerous patients had significant bone loss and osteolysis and likely had some degree of collateral ligamentous compromise at the index revision.34 On the basis of these studies’ findings, it is essential to have intact collateral ligaments, adequate bone stock, and appropriate soft tissue balancing when utilizing PS TKA designs in revision TKA. Therefore, if there is insufficiency of either collateral ligament complex, a more constrained prosthesis design is likely required.35
Varus–Valgus Unlinked Constrained Total Knee Arthroplasty The unlinked VVC design is next in the continuum of increasing constraint. The taller spine and tighter coronal fit within the intercondylar box provide enhanced varus–valgus stability. This post design feature imparts stability by limiting rotation, medial–lateral translation, and varus–valgus angulation (►Fig. 2A–C). In the presence of a completely incompetent medial collateral ligament, excessive stresses encountered by the spine-cam mechanism could lead to the ultimate failure of a VVC implant. The taller and more conforming spine-cam mechanism in VVC implants results in increased stress at both the fixation interface and constraining mechanism of the implant which may lead to early implant loosening or implant failure due to wear of the stabilizing spine. As a result of the increase constraint, stems should be considered for supplemental fixation due to increased forces across the bone–cement interface. Promising results with various VVC designs in the revision TKA have been reported by several authors. A recent study of 114 revision knee replacements with VVC design, showed 96% survivorship at 10 years.36 Similar results with success rates of 70 to 94% have been reported in series from other authors.37–44 In several of these studies, primary and revision The Journal of Knee Surgery
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constraint available in TKA designs are as follows: (1) PCL retaining ; (2) posterior cruciate substitution (PS); (3) varus– valgus constrained, sometimes referred to as semiconstrained or unlinked constrained designs; and (4) hinged or linked constrained designs. The revision prosthesis selected should provide the degree of stability necessary to correct the anticipated instability.
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Fig. 2 (A) Radiographs of a 48-year-old male patient who presented many years after an anterior cruciate ligament reconstruction. (B) A posterior cruciate substituting total knee arthroplasty (TKA) was performed, but soft tissues were poorly balanced. (C) The patient was revised to a varus– valgus constraint TKA and provided excellent medial/lateral stability.
cases were included and, as expected, a trend toward better results in the primary TKA setting was noted. Early results with modern implant designs have not validated the concern regarding the potential disadvantage of increased stress across the bone–implant interface leading to early loosening with the more constrained TKA designs. In the series by Rosenberg et al, only one of 33 patients required rerevision with follow-up ranging from 24 to 84 months although radiolucent lines up to 2 mm were present in nearly 60% of the patients.40 In a series by Nazarian et al reporting on 207 revisions with a follow-up duration ranging from 2 to 6 years, only four femoral components and six tibial components required re-revision.42 Wilike et al reported on 10-year follow-up of 234 VVC TKA revisions performed for soft tissue deficiency. At 10 years, they report 81% survivorship.43 Longer follow-up evaluation of these designs is needed to more clearly understand their long-term durability. Recently, rotating platform (mobile-bearing) unlinked VVC TKA designs have been introduced which offer the potential advantage of decreasing stress at both the spine-cam mechanism as well as the fixation interface.44–46 While fluoroscopic evaluation of axial rotation has shown reduced axial rotation following TKA, it has revealed that there are many in vivo outliers who demonstrate axial rotation magnitudes that exceed the rotational limits of most fixed-bearing designs.47 Jones et al demonstrated that the incorporation of polyethylene-bearing mobility minimizes the transfer of torsional The Journal of Knee Surgery
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stresses to the fixation interface that has been associated with failure of fixed-bearing TKA implants.48 Bearing mobility also reduces rotational stresses on constraining spines, potentially reducing spine wear. In vivo kinematic studies have demonstrated that a rotating platform bearing primarily tracts with the femoral component during axial rotation.49 This allows the constraining spine to remain self-centered within the intercondylar box, reducing rotational stress on the spine. Retrieval studies in failed fixed-bearing TKAs have demonstrated substantial postwear can occur.50 The wear pattern was often rotational and was particularly evident in TKAs with increased constraint, which can be lessened with a mobile-bearing rotating platform. Mobile-bearing designs, however, do add an additional wear interface and with inexperience or in the case of severe instability can add to the complexity of establishing a stable knee.
Linked Hinge Constrained Total Knee Arthroplasty The linked hinge TKA offers the greatest constraint of all implant designs currently used in revision TKA. VVC designs have been very effective in most cases of revision for substantial instability or bone loss. However, in the extreme cases of global instability (severe flexion instability with a massive flexion gap dimension), total loss of collateral ligamentous support, massive bone loss such that collateral ligament attachments have been lost, and in situations with severe posterior capsular insufficiency with uncontrolled
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Fig. 3 (A) Anteroposterior and lateral radiographs of a patient who had a dislocation with a poorly balanced posterior cruciate substituting total knee arthroplasty (TKA). (B) The patient was revised to a larger polyethylene insert that did provided stability. (C) Unfortunately, the patient developed an infection and had significant bone loss on explant. The patient was revised to a linked hinged constrained TKA after clearing the infection.
hyperextension increased constraint using a linked hinge design is indicated. Cases with massive osteolysis, particularly of the distal femur, often lose collateral ligamentous integrity due to loss of the osseous ligament attachments (►Fig. 3A–C). Uncontrolled hyperextension is most commonly observed in patients with paralytic conditions with marked quadriceps weakness in which the patient repeatedly hyperextends the knee to stabilize the limb during the stance phase of gait. Similar to VVC implants, rotating platform linked hinge devices are preferred to fixed bearing designs due to the lower stresses incurred by the implant and fixation interfaces secondary to the presence of bearing mobility. Another subset of patients that benefit from the increased constraint provided by a distal femoral replacing linked hinge device is elderly patients with osteoporosis and severely comminuted supracondylar femoral fractures.51–54 In a study by Berend and Lombardi, 39 patients were reviewed who were treated with a rotating hinge distal femoral replacement; 13 for periprosthetic fractures, one for a distal femoral nonunion, and one for an acute distal femur fracture. They observed an 87% survivorship at 46 months in this series.53 Despite the improved stability provided, linked hinge TKA devices (particularly fixed hinge implants) have a poor historical track record with high rates of loosening, recurrent instability, prosthetic failure, extensor lag, chronic pain, and infection.55–57 Springer et al noted a significant risk of complications including infection, patellar complications, and implant breakage and recommended the utiliza-
tion of distal femoral replacing linked hinge devices with caution.52 Hui and Fitzgerald reported a 23% incidence of major complications, primarily infection and loosening, in their series of 67 fixed hinged arthroplasties.55 In a series by Jones et al reporting on 1 to 3 year results of 108 GUEPAR fixed hinged total knees, 29% of patients had poor results. Prosthetic loosening occurred in 27% of patients, infection in 11%, and 50% patients had patellar complications.56 Other studies have also noted high rates of patellar complications, infection, and even periprosthetic fracture in linked–hinged fixed-bearing TKA.57,58 Results with newer hinge TKA designs which incorporate bearing mobility have shown more promising outcomes.59–63 It is difficult to determine, however, whether improved implant design or better patient selection has led to improved outcomes. Barrack et al reported on 16 salvage revisions with a second generation rotating hinge TKA and compared those to 87 less complicated revision procedures with a VVC design. There were similar outcomes when compared with the less constrained group with no evidence of loosening at 2 to 6 years.59 The series was expanded to 23 patients with 2- to 9-year follow-up and continued to show no evidence of early loosening.60 Barrack’s initial series was further expanded to 30 patients by Jones et al and showed 100% survivorship at 24 to 74 months follow-up.61 Loosening was not present in any patient. In a series of 72 salvage revision TKA procedures with a rotating hinge prosthesis reported by Deehan et al with an average follow-up of 10 years (range, 3–18 years), survival analysis showed 90% implant survival at 10 years and only The Journal of Knee Surgery
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one patient had evidence of aseptic loosening.62 Despite excellent long-term survivorship in this series, 15% of patients complained of a persistent dull ache and 7% have an extensor lag of greater than 5 degrees. It is important to note that even the minor elevation of the joint line in a hinged component can lead to significant loss of mechanical advantage for the quadriceps and should be avoided, as it exacerbates anterior knee pain, extensor lag, knee “buckling,” and actually produces a sense of instability in some patients. One of the benefits of this implant is that balancing the flexion and extension gaps is not required, making joint line restoration somewhat easier. Another series of 24 patients treated with rotating hinge prosthesis showed no evidence of loosening or mechanical failure at a follow-up of 21 to 62 months with a significant improvement in Knee Society scores postoperatively.63 Failure of a rotating hinged prosthesis leaves few reconstructive options. Reimplantation of a modular tumor prosthesis, allograft-prosthesis composite, above-the-knee amputation, and fusion become the remaining options. Therefore, these prostheses should be used only in the elderly low-demand patient population with a limited life expectancy or in extreme cases of instability.
References 1 Meftah M, Ranawat AS, Ranawat CS. Ten-year follow-up of a
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Summary Similar to the goals of primary TKA, revision TKA seeks to restore the function of the knee. Surgeons performing revision TKA must respect the complexity of the procedure and must have a methodical, stepwise approach in the management of the failed TKA. A thorough preoperative history and physical examination are the first step in determining the cause of failure and prevention of complications. Careful assessment of ligament integrity and range of motion, a clear interpretation of imaging modalities, and evaluation to rule out infection must be undertaken. Performing revision surgery without a clear cause of failure is not recommended and often leads to poor results. After determining the cause of failure, careful preoperative planning and meticulous surgical technique is essential to assure an optimal surgical outcome. In revision TKA performed for instability, prosthetic constraint should be titrated according to the deficiencies of the soft tissues after making every attempt to balance the soft tissues to achieve symmetrical flexion and extension gaps. As a general rule, the least amount of constraint necessary to provide adequate stability should be utilized. For this reason, PS TKA devices will provide adequate stability in a majority of cases, as most patients retain the integrity of the collateral ligaments in a revision setting. However, in cases with substantial collateral ligament laxity or severe flexion–extension gap mismatch, a VVC device is recommended. Revision TKA cases with completely incompetent collateral ligaments are a contraindication to use of a VVC device because of the excessive stresses incurred by the stabilizing spine, which will ultimately result in premature implant failure. In these extreme cases, a rotating platform-linked hinge prosthesis will likely be necessary to provide stability. The Journal of Knee Surgery
In cases with massive bone loss, global instability with uncontrolled hyperextension, or comminuted and osteopenic supracondylar periprosthetic fractures, a linked hinge prostheses is similarly indicated.
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Instability after Total Knee Arthroplasty
