THE REVISION KNEE ARTHROPLASTY
The problem total knee replacement SYSTEMATIC, COMPREHENSIVE AND EFFICIENT EVALUATION
K. G. Vince From Northland District Health Board, Whangarei, New Zealand
There are many reasons why a total knee replacement (TKR) may fail and qualify for revision. Successful revision surgery depends as much on accurate assessment of the problem TKR as it does on revision implant design and surgical technique. Specific modes of failure require specific surgical solutions. Causes of failure are often presented as a list or catalogue, without a system or process for making a decision. In addition, strict definitions and consensus on modes of failure are lacking in published series and registry data. How we approach the problem TKR is an essential but neglected aspect of understanding knee replacement surgery. It must be carried out systematically, comprehensively and efficiently. Eight modes of failure are described: 1) sepsis; 2) extensor discontinuity; 3) stiffness; 4) tibial- femoral instability; 5) patellar tracking; 6) aseptic loosening and osteolysis; 7) periprosthetic fracture and 8) component breakage. A ninth ‘category’, unexplained pain is an indication for further investigation but not surgery. Cite this article: Bone Joint J 2014;96-B(11 Suppl A):105–11.
K. G. Vince, MD, ABOS, NZOA, FRCSC, Consultant Surgeon Northland District Health Board, Department of Orthopaedic Surgery, Whangarei, New Zealand. Correspondence should be sent to Dr K. G. Vince; e-mail:
[email protected] ©2014 The British Editorial Society of Bone & Joint Surgery doi:10.1302/0301-620X.96B11. 34531 $2.00 Bone Joint J 2014;96-B(11 Suppl A):105–11.
Evaluation In a memorable exchange from the feature film “A Few Good Men” (1992; Directed by Rob Reiner) Col. Nathan Jessup (Jack Nicholson) is cross-examined by Lt. Daniel Kaffee, a young military lawyer (Tom Cruise) Jessup :“You want answers?” Kaffee: “I think I’m entitled” Jessup :“You want answers?” Kaffee: “I want the truth” Jessup: “You can’t handle the truth” Total knee replacements (TKR) may fail for a variety of reasons, but faced with a patient whose surgery turns out to be problematic, the surgeon must be equipped ahead of time with a system to answer the questions: “why is this patient unhappy with their TKR and can something be done to improve it?” The following is a systematic, comprehensive and in my view efficient system to supply that answer. Systematic Structure. A ‘system’ to evaluate every TKR implies structure, which in turn requires elements or building blocks and a ‘differential diagnosis’ to make up the blocks. The differential diagnosis is the classical medical method used to discriminate between two or more conditions that show similar clinical signs or symptoms. Unlike the triumphant diagnosis of disease, understanding a problem TKR often
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implies shortcomings with the surgery. A failed joint replacement should not be evaluated simply by mental shortcuts, sometimes known as ‘heuristics’.1 Analysis is essential and a worksheet represents one possible scheme (Fig. 1). The diagnostic scheme described here2-4 owes a large debt to John Moreland’s 1988 paper that identified seven mechanisms of failure in TKR.5 Each one was based on the prime requirements for a sound joint replacement. Slight modification and the addition of an eighth mechanism, (mechanism 5: Patellar maltracking and related problems) concludes that a satisfactory TKR will be: uninfected, with an intact extensor mechanism, reasonable flexion and extension; stable, with a centrally tracking patella and sound components that are accurately rotated and well-fixed to a sound tibia and femur. If these criteria are present, it is unlikely that a patient will benefit from revision TKR and an explanation for trouble should be sought elsewhere (Table I).
The Elements Each mode of failure must be clearly defined. Mode
1. The Musculoskeletal Infection Society defines criteria for the diagnosis of the first mode of failure, which is periprosthetic infection.6 Even ‘culture negative infections’ have been specified7 and it is not acceptable to diagnose ‘low grade’ infections as an explanation 105
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Fig. 1 Pre-revision worksheet that lists eight modes of failure in the column on the left with the pertinent data points on the right. This must be completed to diagnose, understand and correct a problem. This is systematic - every patient is assessed by the same system: considering these eight modes of failure in this sequence. It is also comprehensive: even if one diagnosis is established, all eight are considered. The ninth category, ‘unexplained pain’ is a contra-indication to surgery but a reason to re-evaluate the patient.
Table I. Requirements for functional total knee replacement 1 2 3 4 5 6 7 8
No infection Functional extensor mechanism Flexion and extension Stability Centrally located patella Sound fixation Bones intact - no fracture Component intact - no structural failure
for unexplained pain if the strict conditions of the definitions of infection cannot be satisfied. Mode 2. Extensor mechanism deficiency describes loss of efficacy due to loss of continuity (eg rupture) or efficiency (e. g. patellectomy). This category includes transverse patella fractures that result in an ‘extensor lag’, as they do not respond well to fracture fixation.8,9 Like ruptures, transverse fractures are often best treated with allograft reconstruction.10,11 Mode 3. Here, a reasonable range of movement is absent or in other words there is a stiff knee which is easy to diagnose, but can be difficult to understand and treat. Rather than define stiffness by arbitrary limits to movement, (i.e. flexion less than 75°12) the patient should decide if the new joint is unacceptably stiff. The surgeon advises if surgery is appropriate. The stiff TKR may have poor flexion or extension, either with or without pain.13-15 Established stiffness requiring revision TKR should be distinguished from limits to movement in an otherwise functional knee replacement
that results from a patient’s inability or unwillingness to participate in physical therapy. These usually respond to manipulation under anesthesia or relatively minor interventions.16,17 An unflawed TKR made stiff exclusively by scar formation or ‘arthrofibrosis’18 would similarly be expected to fail if revised. By contrast, if a mechanical feature impedes movement and scar tissue ensues, revision may be very useful. There are widely varying opinions regarding the stiff TKR, but it arguably results from multiple factors. Simple fixes are rare.19 Mode 4. Tibial-femoral instability specifies structural unreliability specifically from: soft-tissue failure, excess loading, or as the direct and immediate result of inadequate component position or size. In most cases, all three play a role. Not all unstable TKRs are however, cases of ‘primary instability’. Pain inhibition, extensor rupture, fixed flexion contracture,20 patellar dislocation component loosening with bone loss, periprosthetic fracture or component breakage may render a knee ‘unreliable’ or ‘unstable’; in short, any of CCJR SUPPLEMENT TO THE BONE & JOINT JOURNAL
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the other modes of failure. The corrective surgery required will be fundamentally different for true tibial-femoral instability, if the root causes are to be addressed. When a patient reports ‘instability’, everything else must be considered before primary ‘tibial-femoral’ instability can be diagnosed. Primary tibial-femoral instability can be understood more deeply as: i) coronal plane (varus-valgus) instability, ii) plane of movement instability (resulting from fixed flexion contractures and recurvatum) or as iii) ‘flexion’ instability,21,22 due to a relatively larger flexion gap. Varus-valgus instability requires attention to alignment and the constraining action of ligaments or implants. ‘Buckling’ in the plane of movement (apart from extensor rupture and patellar maltracking) usually results from extensor mechanism insufficiency or flexion contracture. Flexion instability results from a flexion gap that is larger than the extension gap where a polyethylene insert has been selected to permit full extension. Revision to equalise the gaps is definitive. For all cases of primary instability, when soft-tissue function cannot be restored, mechanical constraint is indicated.23-25 Mode 5. This includes problems related to patellar tracking and malrotation. If the patella has dislocated or subluxed, then revision invariably requires a correction of the rotational position of the tibial and femoral components. The medial-lateral position of femoral26 and patellar27 components should also be considered. Maltracking may explain patellar component loosening, wear and vertical fractures. For each of these, the patellar button is designed to stay in the femoral trochlear groove while the extensor mechanism and the patellar bone dislocate, causing excess wear or parting of the component from the patella.28-30 Mode 6. Loosening includes osteolysis plus failed ingrowth in uncemented devices. Loosening, especially with bone loss from osteolysis may render a TKR unstable, even if ligaments are intact. Restoration of bone and fixation, not constraint, restore stability. Mode 7. Periprosthetic fractures may be treated by fracture fixation or revision. Though dramatically unstable, they are not cases of primary tibial-femoral instability. Mode 8. Late instability, though often attributed failure of a posterior cruciate ligament almost always results from polyethylene wear and so is actually a manifestation of the eighth mode, breakage or structural failure. Caveats. Proceed with caution when none of the above eight diagnoses can be confirmed. Revision for unexplained pain has long been recognised as likely to fail.31 Unusual diagnoses such as neuroma32,33 and popliteus tendon impingement34 may be considered, but at a minimum, surgeons should look for pain originating beyond the knee joint, referred from an arthritic hip or spinal radiculopathy. Note that ‘malrotation’ and ‘malalignment’ contribute to several diagnoses, but are not actual diagnoses themselves. Experienced surgeons will recognise that revision of a VOL. 96-B, No. 11, NOVEMBER 2014
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dislocating patella is a fundamentally different surgery from revision of a stiff TKR although internal rotation of tibial and femoral components may have caused both. In the absence of symptoms, revision surgery is difficult to justify for undesirable component position alone.
The Algorithm The modes, considered sequentially, can constitute a diagnostic algorithm. Sepsis is first on the list, consistent with its importance and the reminder that it must be ruled out in all painful TKRs. Extensor compromise including rupture, is second because it is easy to diagnose and perhaps as feared as sepsis. Stiffness can be diagnosed, if not understood, easily; it is included or eliminated early as the cause of trouble. Tibial-femoral instability is the fourth and slightly more complex category. As described above, not all knees that a patient might describe as ‘unstable’ are cases of primary tibialfemoral instability. When a patient reports instability, buckling or ‘giving way’, all sources of pain must be considered, plus hip contractures and neurological extensor impairment, before concluding that the diagnosis is primary tibial-femoral instability. Then, primary instability can be further categorised as: coronal, plane of movement, flexion or a combination. These first four diagnoses are strongly suspected, if not confirmed, by the history and physical examination. The subsequent four require imaging. For example, the fifth category, patellar tracking problems, are best visualised with patella-femoral radiographs. Loosening is sixth, forcing us to consider other possibilities before diagnosing the most common mode of failure. Peri-prosthetic fracture, the seventh mode of failure, is clear on radiographs. True component breakage, distinct from wear and loosening, is a rare but important consideration. No matter which mechanical mode of failure may be present it will always have been important to rule out the first diagnosis of sepsis. If no explanation for problems can be identified after these eight modes have been considered, plans for surgical intervention are best put aside, while problems outside the joint are considered. This is a good juncture to reconsider the possibility of referred pain from the hip or spine as well as chronic regional pain syndrome. The patient’s expectations of arthroplasty, especially if pre-surgical radiographs reveal minimal arthritic change, may have led to dissatisfaction. In such a case, the results of revision are likely to be even more disappointing. Depression has been associated with poor results after arthroplasty, but it is always difficult to ascertain whether low mood is a cause of dissatisfaction, or the result of chronic pain and disillusionment. While isotope bone scans are usually so non-specific as to be of little help, a negative bone scan in this situation argues strenuously against further surgery. Revision surgery is likely to succeed only when objective findings support one of the eight categories above.
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The process An organised system requires a consistent routine for collecting data from the history, physical examination, imaging and laboratory investigations. Some surgeons find it useful to obtain old operative reports. Specifically important information from the history and physical examination are described below. Imaging Imaging is particularly important when structural failure is the problem. Three standard views, with strict adherence to radioglogical technique are essential. A single-leg weight-bearing radiograph depicts changes in component position (loosening) and coronal plane instability. Serial radiographs will identify change in component position, diagnostic of loosening. The lateral view, if performed with a single-leg weight-bearing technique, can quantify flexion deformity and recurvatum as well as component position. The patellar-femoral joint must be imaged to assess tracking: most surgeons rely on the Merchant view.35 Alignment is a frequent causative factor in cases of instability, patellar maltracking and aseptic loosening and can only be evaluated accurately with full length radiographs that show the hip, knee and ankle on the same study. The rotational position of the limb is important for these views.36 If long cassettes are not available, then a full AP femur (showing the femoral head and knee joint) plus another full view of the tibia will suffice to evaluate the mechanical axis. Full-length images reconstructed from CT scanning, where the patient is supine, are less useful than weightbearing radiographs. CT scans are useful prior to every revision knee arthroplasty to quantify the rotational position of components and to evaluate osteolysis. 37 Internal rotation position has profound implications for anterior knee pain,38 patellar tracking problems,39 stiffness14 and instability.40 There will undoubtedly be further understanding of the nuances of rotational positioning in the future, as implant designs are better able to replicate functional anatomy. Isotope imaging, though very sensitive is non-specific and rarely useful, except perhaps in the evaluation of a patient with pain that has not been explained after the basic assessment. Diagnostic arthroscopy will not be useful to the experienced arthroplasty surgeon as virtually every cause of failure can be diagnosed by other, simpler means. Combining information. Specific data points are essential to diagnose each mode of failure and plan a successful revision. Periprosthetic infection requires clinical suspicion by history and physical examination plus erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) tests from peripheral blood. If suspicion or inflammatory markers are elevated, fluid aspirated from the joint must be sent for cell count, differential and culture. These will be interpreted according to published guidelines.41,42 Extensor compromise or rupture is quan-
tified by the amount of extensor lag in degrees, in conjunction with passive flexion and extension. Stiffness is quantified the same way and should include the presence or absence of pain as well as the amount of movement prior to arthroplasty. Varus-valgus instability should be recorded as the arc from maximum varus to maximum valgus with load applied, both in full extension where the posterior capsule may cloud the picture by conferring some coronal plane stability even without collateral integrity and in 30° flexion to relax the posterior structures. Buckling from fixed flexion contracture probably belongs in the category of the stiff knee above as surgical correction requires similar techniques. Buckling from recurvatum requires the same data: joint movement and gait evaluation. Flexioninstability is mainly diagnosed from the history, with superior flexion and a flexion gap that can be distracted with the knee at 90° of flexion while the patient is on the edge of the examination table. Patellar maltracking is apparent on the Merchant35 (or similar) patellar-femoral radiograph. Loosening is diagnosed when a component has subsided or when circumferential radiolucent lines are present. Osteolysis is so intimately involved with the aetiology of aseptic loosening, that it can be considered as a more severe stage of the same mode of failure. Accordingly, osteolysis should be considered in every case of loosening, and significant osteolysis can be accepted in support of the diagnosis of aseptic loosening or impending loosening.43 Peri-prosthetic fractures are suspected by history and confirmed by the radiographs. Breakage or structural failure of the implant may be difficult to diagnose. It is usually the cause of late onset instability and may be apparent on radiographs. Mode 9. Pain without a diagnosis, is a mandate for further investigation, contemplation and patience but a contra-indication to surgery. It is not, by itself, an indication of psychological problems. This is the time to reconsider the possibilities of hip or spine pain. If one of the eight diagnoses has not been established, it may be useful to review pre-surgery radiographs to confirm the presence of severe arthritis. It is the rare patient who would prefer a TKR to their own knee when only minimal cartilage loss was present.
Comprehensive: consider all eight Comprehensive means that all eight possibilities will be considered for every patient; even after one obvious cause is identified. For example, any TKR with structural problems may also be infected. A stiff TKR may have a ruptured extensor mechanism or instability. The unstable knee may also have a dislocating patella. Accordingly, it is necessary to assign major and minor diagnoses to a failed TKR to ensure that all underlying pathology is treated with revision. In a busy practice, with many demands on a surgeon’s attention, facile and potentially incomplete diagnoses are attractive but hazardous. To prematurely conclude that a CCJR SUPPLEMENT TO THE BONE & JOINT JOURNAL
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Fig. 2a
Fig. 2b
Fig. 2c
Figure 2a - Schematic representation of the lower limbs and pelvis of a seated figure (left), which includes patients with flexion instability, a flexion gap that is lax compared with the extension gap or experience problems while loading the knee in a flexed position, such as rising from a seated position or walking up or down stairs. Zoom on right, vertical arrow indicates excursion between the tibial surface and the posterior femoral condyles. Horizontal striped arrow indicates tibial-femoral instability. Figure 2b - Frames from a clinical video clip of a patient with flexion instability. The patient is seated on an examination table, with quadriceps relaxed. Arrow indicates level of the inferior incision, as an arbitrary landmark. Figure 2c - When the patient contracts the quadriceps, the second arrow indicates the level of the inferior pole of the incision. The contraction has not resulted in knee extension, but, closure of the lax flexion gap.
TKR is simply stiff or loose may lead to poor results from surgery. There is a lot at stake when revision TKR is contemplated.
Efficiency: streamlined data collection Many strategies can be used for medical interviews, but it is common to begin with an open-ended question, such as: ‘What seems to be the problem?’ The patient might reply: ‘Pus is draining from my knee’, making the diagnosis obvious, but the process incomplete. Similarly: ‘I can't straighten my knee’, or ‘I can’t bend it’. More commonly, the patient will report pain, swelling, stiffness, giving way or a sense that ‘things just don’t feel right’. VOL. 96-B, No. 11, NOVEMBER 2014
A useful second question involves whether the knee replacement was ever successful after surgery. If there was never a period of good function and pain relief, the automatic third question is whether the current pain resembles the pain prior to the surgery or if it is new and different pain. Pain that's unchanged by surgery may originate outside the knee. A new but different pain commonly results from sepsis, stiffness due to component size and position with or without chronic regional pain syndrome or failed ingrowth. Late onset of pain after a period of good function indicates that something has changed in a previously good TKR: infection, loosening, peri-prosthetic fracture and breakage or catastrophic wear are likely explanations.
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The standard questions taught to every medical student about pain now apply: i.e. location, severity, duration, frequency and quality followed by exacerbating and ameliorative factors. The answers can be evaluated in a biomechanical context. Pain rising from a chair, or ascending or descending stairs are associated with increases in the joint reaction force. This may point to the extensor mechanism, the fixation interface or intra-capsular tension from an effusion. This general inquiry about pain is followed by specific questions pertinent to other problems the patient may report: swelling, stiffness, giving way, weakness or a sense that things are ‘just not right’. Questions intended directly to establish the clinical suspicion of infection include whether the wound healed smoothly, whether hospitalisation was prolonged, if anyone expressed concern about possible infection and if nonprophylactic antibiotics were prescribed after surgery. Either clinical suspicion of infection or laboratory elevations of the ESR or CRP – indicate that the knee should be aspirated for cell count, leukocyte differential and culture and sensitivity.44 Physical examination of the patient with a problem TKR could be exhaustive and yet there are specific areas that yield indispensable information. Gait evaluation, specifically the characteristic coxalgic gait or shift of the centre of gravity over a painful hip, is often the first indication that pain may be referred from the hip.45 Instability and alignment will be best understood with the patient walking. Watching them rise from a chair or step up onto a foot stool reveals a great deal about knee function and other problematic joints. Internal rotation of the femoral component, as well as hip stiffness, can be revealed by internal rotation of the flexed hip. While the patient sits on the edge of the exam table with knees flexed to 90o and legs relaxed, internal rotation of the tibial component usually results in apparent external rotation of the tibia and foot. This is the best position to assess the stability of the flexion gap, and may be the only way to objectively demonstrate flexion instability (Fig. 2). Important information specific to our protocol includes swelling, effusion, warmth, point tenderness and movement expressed in degrees as flexion, extension and lag. Instability in the coronal plane, should be recorded in full extension and a few degrees of flexion where the posterior capsule is relaxed.
Conclusions Every patient with a problem arthroplasty should be evaluated with the same disciplined system. This includes a standard differential diagnosis with well-defined modes of failure, which may serve as reliable indications for surgery. A standard system would enhance reports of surgical results in clinical series and registries.46 Systematic means considering the possibilities in a similar sequence and collecting the same data methodically for each patient. Comprehensive means that even if one diagnosis is identified
that all the others are considered: some failed TKRs may have more than one problem. Efficiency comes not only from adhering to this routine, but in creating a sequence of questions for the clinical interview that is followed in each case - one that is designed to evaluate each possibility in turn. Revision surgery is the opportunity to correct the causes of failure. It should never be simply repeat surgery. 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 paper is based on a study which was presented at the 30th Annual Winter 2013 Current Concepts in Joint Replacement® meeting held in Orlando, Florida, 11th – 14th December.
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