Constrained implants with intra-medullary fixation are expedient for complex TKA. Constraint is associated with loosening, but can correction of deformity mitigate risk of loosening?

Primary TKA's with a non-linked constrained prosthesis from 2010-2018 were identified. Indications were ligamentous instability or intra-medullary fixation to bypass stress risers. All included fully cemented 30mm stem extensions on tibia and femur. If soft tissue stability was achieved, a posterior stabilized (PS) tibial insert was selected.

Pre and post TKA full length radiographs showed.

77 TKA's in 68 patients, average age 69.3 years (41-89.5) with OA (65%) post-trauma (24.5%) and inflammatory arthropathy (10.5%).

Pre-op radiographs (62 knees) showed varus in 37.0% (HKAA: 4^o-29^o), valgus in 59.6% (HKAA range 8^o-41^o) and 2 knees in neutral.

13 cases deceased within 2 years were excluded. Six with 2 year follow up pending have not been revised. Mean follow-up is 6.1 yrs (2.4-11.9yrs).

Long post-op radiographs showed 34 (57.6%) in central KZ (HKKA 180^o +/- 2^o)^.

Thirteen (22.0%) were in mechanical varus (HKAA 3^o-15^o) and 12 (20.3%) in mechanical valgus: HKAA (171^o-178^o)

Three failed with infection; 2 after ORIF and one with BMI>50. The greatest post op varus suffered peri-prosthetic fracture. There was no aseptic loosening or instability.

Only full-length radiographs accurately measure alignment and very few similar studies exist. No cases failed by loosening or instability, but PPF followed persistent malalignment. Infection complicated prior ORIF and elevated BMI.

This does not endorse indiscriminate use of mechanically constrained knee prostheses. Lower demand patients with complex arthropathy, especially severe deformity, benefit from fully cemented, non-linked constrained prostheses, with intra-medullary fixation. Hinges are not necessarily indicated, and rotational constraint does not lead to loosening.

The most recent Australian registry has a database of 547,407 knee arthroplasties, having added over 52,000 in 2016. Total knee arthroplasties (TKA) comprise 83.8%, revisions (RevTKA) 8.1% and “partials of all types” 8.1%. Since 2003, the percent of TKA has increased from 76.7%, RevTKA has stayed stable and partial replacements have declined from 14.5%. In the last year, however, TKA declined slightly.

There is a slightly higher percentage of women (56.1%) undergoing TKA and this has remained very stable since 2003. Revision rates are slightly higher for men. Percentages of the youngest (<55) and oldest (>85) are small and stable. The 75–84 year olds have declined as 55–74 year olds have increased. This represents a gradual shift to earlier TKA surgery. More patella are resurfaced and this is a gradual trend with a cross over in 2010 when half were resurfaced. Computer navigation is progressively more popular and now accounts for almost 30% of cases. Cement fixation is also increasing and accounts for about 65% of cases. Crosslinked polyethylene is gradually replacing non crosslinked and in 2014 was used in 50% of cases.

Revisions are performed most commonly for loosening and infection. Revision rates correlate directly with age. Loosening is the most common indication for revision in both genders, but males have a distinctly higher revision rate due to infection. Revision rates are slightly higher in all forms of mobile bearing than fixed bearing.

Minimally constrained (cruciate retaining) devices are used in the majority of TKAs. Posterior stabilised implants are in slight decline, having peaked in about 2008–2010. Minimally constrained implants are in slight decline as medial pivot/medial congruent devices have been used more frequently. Revision rates are similar amongst all three implant types: PS implants are revised at a slightly higher rate. When an early Medial Pivot (MP) implant is excluded the newer version has better results. The reasons for revision are similar amongst all 3 groups with slightly higher loosening rates for PS designs. (Could this represent backside wear with older locking mechanisms, surface finish and non crosslinked poly?) The MP designs had slightly higher revision rates for “pain”, which is not recognised as a reasonable indication for revision.

Revision rates are steadily higher for TKAs without patella resurfacing over 16 years, but the questions as to whether: i. the surgeries were secondary resurfacings or full revisions or ii. if secondary resurfacings eliminated pain are unknown. The combinations at greatest risk of revision were a posterior stabilised or medial pivot arthroplasty without patellar resurfacing. Cementless fixation leads to a higher revision rate.

If age and computer navigation are evaluated in terms of revision rates, young patients with and without computer navigated arthroplasties failed at the highest rates, distinct from patients >65. However, if failure rates due only to loosening are evaluated, then computer navigation leads to a lower revision rate in the <65 group. This has been interpreted as the protective effect of better component position that only shows up in patients who use the arthroplasty more aggressively.

Patient specific instrumentation (PSI) or Individual Designed Instrumentation (IDI) were revised at marginally higher rates than conventional instrumentation. Crosslinked polyethylene appears to be superior at 12 years (CRR= 4%) versus non crosslinked polyethylene (CRR>7%). This is the result of fewer failures due to loosening with crosslinked poly. The superiority of crosslinked poly was greater in the younger, more active patient.

Clinical cases will be presented to a panel of experienced arthroplasty surgeons to illustrate how principles tempered by experience, are applied to challenging problems. (request pertinent additional material from kellyvince@mac.com)

“The shortest distance between two points is a straight line.” This explains many cases of patellar maltracking, when the patellar track is visualised in three dimensions. The three-dimensional view means that rotation of the tibia and femur during flexion and extension, as well as rotational positioning of the tibial and femoral components are extremely important. As the extensor is loaded, the patella tends to “center” itself between the patellar tendon and the quadriceps muscle. The patella is most likely to track in the trochlear groove IF THE GROOVE is situated where the patella is driven by the extensor mechanism: along the shortest track from origin to insertion. Attempts to constrain the patella in the trochlear groove, if it lies outside that track, are usually unsuccessful. Physiologic mechanisms for tibial-femoral rotation that benefit patellar tracking (“screw home” and “asymmetric femoral roll-back”) are not generally reproduced.

The true results of revision total knee arthroplasty (TKA) are not fully understood, for a variety of understandable reasons. But it is has been clear for decades that revision without a diagnosis is likely to fail. The evaluation of the problem TKA should be systematic (follow the same scheme every time) and comprehensive (all possibilities should be considered even if one diagnosis seems obvious).

Evaluation begins, as with all of medicine with a list of possible causes: the mechanisms of failure. John Moreland was the first to describe a coherent system which needed only one simple addition to be complete: 1.) Prosthetic joint infection; 2.) Extensor disruption; 3.) Patella and malrotation; 4.) Loose; 5.) Component breakage; 6.) PP fracture; 7.) Poor motion; and 8.) Tibial femoral instability.

Evaluation begins with the history, where 10 questions in particular are useful: 1.) What seems to be the problem? 2.) Was the “knee” ever successful after surgery? If there was never pain relief, is the current pain, the same or different? 3.) Standard pain quality questions - Location, duration, frequency, quality, exacerbating, ameliorating. 4.) Swelling? 5.) Stiffness? 6.) Giving way? 7.) Weakness? 8.) Things “just don't feel right”? 9.) Possible sepsis questions - Fever, chills, sources, primary TKA healing. 10.) Mood, social situation?

The physical exam should cover these ten points: 1.) Active extension; 2.) Rising from chair; 3.) Gait: hip, knee alignment, knee instability; 4.) Hip (internal rotation); 5.) Inspection; 6.) Tenderness; 7.) ROM; 8.) Stability (extension and 30–45 degrees flexion; 9.) Sitting on edge of exam table (knee at 90 degrees); and 10.) Step up on low stool (stair).

Investigations include: 1.) ESR + CRP; 2.) CBC; 3.) HGB- anemia; 4.) Lymphocytes- nutrition; 5.) GGT- alcohol abuse; 6.) Albumen- nutrition; 7.) HbA1c- diabetic control.

Imaging includes: 1.) Single leg weightbearing AP; 2.) Lateral; 3.) Merchant; 4.) Full length (hip-knee-ankle); 5.) AP pelvis; 6.) CT scan; and 7.) (Technitium bone scan).

In general, “alignment” refers to the position of all components in three dimensions. This discussion is limited to “varus-valgus” (v-v) alignment, or angulation in the frontal plane. This is largely determined by rotational position of the tibial and femoral components about the “z” (antero-posterior) axis. The earliest paper to note the importance of alignment, described only “valgus” on short x-rays.

It is difficult to argue that knee alignment is irrelevant, as angulation increases, so does the lever arm at the knee. (Biomechanics) Alignment is relevant to the development of osteoarthritis, most likely as the result of load on the medial compartment with varus alignment. (Natural History of OA) The first knee arthroplasties were an attempt to resurface worn cartilage with biological tissue and then non-biological material. Alignment and biomechanics were not considered. (History)

Frontal plane alignment can be depicted as “anatomic” (the angle between the femoral and tibial canals) on short radiographs or “mechanical” on full-length radiographs. Mechanical alignment may be reported in degrees or distance. Degrees describes the angle between a line from center of femoral head to center of knee (MA of the femur) with the line from center of knee to center of ankle (MA of tibia.) Alternately if a line is drawn form the center of the femoral head to the center of the ankle, MA may be described as the distance from the center of the knee to this axis along the joint line. Sometimes this is depicted by sectors in the knee. “Mechanical alignment” is a method of describing the angulation of the knee, not strictly a surgical technique.

Long radiographs: Short radiographs, though perhaps cost effective in most clinical settings, are unreliable images for studies of alignment. Physiologists and astute surgeons have always considered the entire limb. When clinicians applied full-length radiographs to clinical practice, along with navigation technology, assumptions evolved about the most desirable alignment of an arthroplasty. Arbitrarily, a neutral mechanical axis, or a straight line from the centers of the hip, knee and ankle was promoted. This also means that a line from hip to ankle would pass through the center of the knee. Many surgeons have entertained the erroneous concept that a “neutral mechanical axis” represents “normal human alignment: it does not. Others contend that a neutral mechanical axis necessarily means that there will be equal load on medial and lateral compartments: it will not.

Received wisdom about the necessity of a neutral mechanical axis has been questioned and yet malalignment and pre-operative deformity both appear to contribute to failure.

Stability is clearly important, because it limits deviations in alignment, and a range of alignments are probably highly functional, just as the knee may be loaded in a variety of directions. Dynamic features of patient activity are undoubtedly important, as is pre-operative deformity.

There is a difference between “functional instability” of a total knee arthroplasty (TKA) and a case of “TKA instability”. For example a TKA with a peri-prosthetic fracture is unstable, but would not be considered a “case of instability”. The concept of “stability” for a TKA means that the reconstructed joint can maintain its structure and permit normal motion and activities under physiologic loads. The relationship between stability and alignment is that stability maintains alignment. Instability means that there are numerous alignments and almost always the worst one for the loading condition. In the native knee, “instability” is synonymous with ligament injury. If this were true in TKA, then it would be reasonable to treat every “unstable TKA” with a constrained implant. But that is NOT the case. If the key to successful revision of a problem TKA is understanding (and correcting) the specific cause of the problem, then deep understanding of why the TKA is unstable is essential. A case of true “instability” then, is the loss of structural integrity under load as the result of problems with soft tissue stabilizing structures and/or the size or position of components. It is rare that ligament injury alone is the sole cause of instability (valgus instability invariably involves valgus alignment; varus instability usually means some varus alignment and compromised lateral soft tissues). There will be forces (structures) that create instability and forces (structures) that stabilise.

There are three categories of instability: Varus-valgus or coronal: Assuming that the skeleton, implant and fixation are intact. These are usually cases that involve ligament compromise, but the usual cause is CORONAL ALIGNMENT, and this must be corrected. The ligament problem is best solved with mechanical constraint. Gait disturbances that increase the functional alignment problems (hip abductor lurch causing a valgus moment at the knee, scoliosis) may require attention of additional compensation with re-alignment. Plane of motion: Both fixed flexion contractures and recurvatum may result in buckling. The first by exhaustion of the quadriceps (consider doing quadriceps “lunges” with every step) and the second because recurvatum is usually a compensation for extensor insufficiency. The prototype for understanding recurvatum has always been polio. This is perhaps one of the most difficult types of instability to treat. The glib answer has been a hinged prosthesis with an extensor stop but there are profound mechanical reasons why this is flawed thinking. The patient with recurvatum instability due to neurologic compromise of the extensor should be offered an arthrodesis, which they will likely decline. The simpler problem of recurvatum secondary to a patellectomy will benefit from an allograft reconstruction of the patella using a modified technique. A common occurrence is obesity with patellofemoral pain, that the patient has managed with a “patellar avoidance” or “hyperextension gait”. Plane of motion instability is a problem of the EXTENSOR MECHANISM DEFICIENCY. Flexion instability. This results from a flexion gap that is larger than the extension gap, where a polyethylene insert has been selected that permits full extension but leaves the flexion gap unstable. These patients achieve remarkable flexion easily and early, but have difficulties with pain and instability on stairs, with recurrent (non-bloody) effusions and peri-articular tenderness. Revision surgery is necessary. Flexion instability may also occur with posterior stabilised prostheses. So-called “mid-flexion” instability is a contentious concept, poorly understood and as yet, not a reported cause for revision surgery distinct from “FLEXION INSTABILITY”. Flexion instability is a problem of GAP BALANCE.

No, Neutral mechanical axis has never been regarded as “necessary” to the success of TKA. In fact it has never been established as “ideal” with published data. Tibial femoral alignment after TKA is important, but it is also an issue that we do not understand completely. Neutral mechanical alignment refers to the relationship between the mechanical axes of the femur and tibia as shown on full length radiographs. “Neutral” means that these axes are collinear, i.e. that a line may be drawn from the center of the hip to the center of the ankle and it will intersect the center of the knee joint. The allure of the “straight line” has led many surgeons to regard a neutral mechanical axis as “perfection” for TKA surgery, but indeed, it is not the usual “normal” alignment for most human knees, nor is it the target for many conventional knee replacements. The “neutral mechanical axis” represents OVERCORRECTION for most knees. Moreland demonstrated in 1987 that few human knee joints are naturally aligned “in neutral”, but with the line from center of hip to center of ankle passing through the medial compartment. This tendency to relative varus mechanical axis in most human knees was corroborated by Bellemans et al in 2012. They substituted the word “constitutional varus” for what would otherwise be known as “normal alignment”.

In general, patients with pathologic or significant varus alignment, whose arthroplasties have been performed competently, are at greatest risk for failure by wear, osteolysis and loosening. This is the prototypical failure mechanism that pre-occupied the surgeons responsible for making knee arthroplasty successful in the 1970s. The first paper to identify varus TKA alignment and failure due to loosening was Lotke and Ecker in 1977. They worked from short radiographs and ushered in an era of careful attention to valgus TKA alignment-not neutral alignment. Correction of varus deformity combined with ligament balancing was probably responsible for making condylar type knee arthroplasties work durably in the early days.

Full length radiographs, used by Kennedy and White in 1987 to study alignment in unicompartmental arthroplasties, provide a more sophisticated method of evaluating knee alignment. These studies must be aligned with correct rotation to be valid. Computerised navigation was probably responsible for some surgeon's dedication to the neutral mechanical axis. The study of Parratte et al from Mayo has received much attention and argued that a neutral mechanical axis did NOT improve success rates at 15 years. It should be noted that these TKA's were expertly performed and even the less well-aligned cases were not “excessively” malaligned. This study does not state that alignment is irrelevant to the success of TKA, but rather that a range of alignments (with stability) might be expected to produce a durable arthroplasty.

Concurrent with these developments has been an interest in “under-correcting” knee deformity or allowing osseous anatomy (with compensation for cartilage loss) guide component position. In truth, it is inaccurate to describe conventional “align and balance” techniques as necessarily seeking a neutral mechanical axis. Most classical alignment techniques do, however, alter the angle of component position from the original articular surface angles and theoretically may not function as well with the native soft tissue environment. Surgeons who would align the TKA identically to the arthritic knee may credit previous generations with improving the technology such that this is a possibility. If every patient is to be aligned with this technique, however, this suggests that soft tissue pathology does not exist. As with all complex issues, glib answers are to be avoided and deep analysis is appropriate.

Some DEFINITIONS are necessary: “STEMS” refers to “intramedullary stem extensions”, which may be of a variety of lengths and diameters, fixed with cement, porous coating or press fit alone and which may be modular or an inherent part of the prosthesis. The standard extension keel on the tibia does not qualify as a “stem (extension)”. COMPLEX implies multiple variables acting on the end result of the arthroplasty with the capability of inducing failure, as well as necessary variations to the standard surgical technique. A lesser degree of predictability is implied. More specifically, the elements usually found in an arthritic knee and used for the arthroplasty are missing, so that cases of COMPLEX primary TKA include: Soft tissue coverage-(not relevant here), Extensor mechanism deficiency-patellectomy, Severe deformity, Extra-articular deformity, Instability: Varus valgus, Instability: Plane of motion, Instability: Old PCL rupture, Dislocated patella, Stiffness, Medical conditions: Neuromuscular disorder, Ipsilateral arthroplasty, Prior incisions, Fixation hardware, Osteopenia, Ipsilateral hip arthrodesis, Ipsilateral below knee amputation, etc.

Complexity includes MORE than large deformity, i.e., success with large deformity does NOT mean success with constrained implants regardless of indication. In addition, the degree of constraint must be specified to be meaningful. NECESSARY presumably this means: “necessary to ensure durable fixation in the face of poor bone quality or more mechanically constrained” and SUFFICIENT suggests that stems, by themselves or in some shape of form, by themselves “will ensure success (specifically here) of fixation”. If we can start with the second proposal, that STEMS are SUFFICIENT for success the answer is: “NO”, many more aspects of surgical technique and implant design are required. Even if all other aspects of the technique are exemplary, some types of stems or techniques are inadequate, e.g., completely uncemented, short stem extensions. The answer to the first proposal is: “YES, in many cases”. The problem will be to determine which cases. There are philosophical analogies to this question that we already know the answer to.

ANALOGY: Is a life-raft necessary on a boat? Yes, you may not use it, but it is considered necessary. Is a life-raft “sufficient” on a boat? No, other problems may occur. Are seat belts necessary? Are child seats necessary? The AAOS already has a position on child restraints, an analogous situation, where a party who cannot control their situation (anesthetised patient/ child) functions in the care of a responsible party. The objection may be argued in terms of cost saving by NOT using increased fixation. A useful analogy, (that would of course require specific analysis), is that of patellar resurfacing: universal resurfacing is cost-effective when considering the expense of even a small number of secondary resurfacings. Of course a complex arthroplasty that requires a revision procedure is far more expensive than secondary patellar resurfacing and so universal use of the enhanced fixation in the face of increased constraint makes sense. The human cost of revision surgery tips the balance irrefutably.

DANGER-We must avoid the glib conclusion, often based on poor quality data, that constrained implants do not need additional intramedullary fixation (with stem extensions). When “complexity” is involved, complex analysis is appropriate to select the best course.

The term mid-flexion instability has entered the orthopaedic literature as a concept, but has not been confirmed as a distinct clinical entity. The term is used freely, sometimes as a synonym for flexion instability. However, the terms need to be clearly separated. A cadaver study published in 1990 associated joint line elevation with decreased stability at many angles of flexion, but that model was not typical of clinical scenarios. The literature is considered and it is proposed that the more common entity of an uncorrected flexion contracture after a measured resection arthroplasty technique is more likely to produce clinical findings that suggest instability mid-flexion.

It is proposed that the clinical scenario encountered is generalised instability, with the appearance of stability in full extension from tight posterior structures.

This paper seeks to clarify whether mid-flexion instability exists as an entity distinct from other commonly recognised forms of instability.

Cite this article: Bone Joint J 2016;98-B(1 Suppl A):84–8.

Knee replacements may be unstable in the: 1. Plane of motion instability, due to recurvatum or buckling (in flexion). 2. Coronal plane or varus-valgus instability and 3. Flexed position. The third, flexion instability, has been well described and is characterised clinically by early, easy, superior flexion that is then compromised by difficulties with ascending and descending stairs, recurrent effusions and peri-articular tenderness. This “flexion instability” results generally from a flexion gap that is more spacious than the extension gap, where the polyethylene insert has been selected to permit full extension.

The term “mid-flexion” instability should not be used as a synonym for “flexion instability”. The concept of mid-flexion instability implies that the knee is stable in extension and stable in flexion (90 degrees) but unstable at points in between. The most common error in assessment probably occurs when surgeons observe stability to varus-valgus stress with the knee locked in full extension, where it is not appreciated that the posterior structures are tight and stabilising the knee. Once the knee if flexed enough to relax these structures, the true “flexion instability is revealed. This is not “mid-flexion” instability.

It is conceivable, that an arthroplasty might be designed where the geometry of the femoral condylar curve is such a large, recessed radius that the collateral ligaments are tight in both full extension and 90 degrees of flexion, but unstable in between. There have been marketing allegations that one product or another has been designed in a way to result in “mid-flexion instability. The only published information is based on finite element analysis models.

There is scant literature on “mid-flexion” instability”. Laboratory investigations with cadavers, concluded that proximal elevation of the joint line may create “mid-flexion” instability as a result of altering collateral ligament function. Computer models have questioned this effect. One clinical report describes “mid-flexion” (rotational) instability in a revision arthroplasty. So-called “anatomic alignment”, posterior stabilization and resection of distal femur to correct flexion contractures have been alleged to cause “mid-flexion” instability.

“Expert opinion” is the lowest totem on the academic pole- and yet, “evidence based” medicine does not always provide us answers for the particular, the unusual clinical problem. Well-controlled studies are precisely that: “well controlled”. Life may be randomised, but falls short of being “well controlled”.

The challenge and honor of moderating a panel of experienced and articulate colleagues is to bring out “how they think” and how they formulate a plan for complex cases. The panel members are not only experienced practitioners, but they are the authors of studies that shape our profession. What are the limits to the studies they have published? What insight can they provide us to help understand “level 1” data more astutely? What biases and assumptions support their methods? Nothing achieves that with greater clarity than presentation of complex cases to an accomplished panel.

Several ordinary clinical problems are presented to establish current practice, followed by the unexpected outcomes to illustrate how experts deal with adversity.

Despite the widely accepted advantages of total knee arthroplasty surgery, not all patients are completely satisfied. This was initially reported with studies from the Swedish Registry and indicates room for improvement in our craft. But who says this is a “growing concern”? First of all are the third party payers and government agencies who would like to curtail expenditures and retain funds. Next are manufacturers promoting new, and one would hope, improved products and finally surgeons similarly promoting new techniques.

But who are the minority of dissatisfied patients and why are they unhappy? There is no reduction in demand for arthroplasty surgery by patients worldwide.

Flexion instability is a well-defined, though often difficult to diagnose, type of TKA instability. It may also complicate posterior stabilised arthroplasties. It is one of three modes of tibial-femoral instability along with: 1. Varus-valgus or coronal plane instability and 2. Instability in the plane of motion that results from either fixed flexion contracture and buckling or recurvatum and collapse. The issues for correction of coronal instability are generally alignment and either ligamentous balance or constraint. For plane of motion instability it is full extension without hyperextension and restoration of extensor mechanism power. The issues for flexion instability are basically balanced flexion and extension gaps.

The diagnosis of flexion instability is made by history and physical examination. These patients, with a more spacious or lax flexion gap, initially do extremely well following surgery, achieving flexion rapidly and comfortably. They progress within months however, to a condition of chronic swelling and tenderness of peri-articular soft tissue, recurrent effusion and a feeling of unease up and down the stairs, as well as getting up out of a chair: anything that stresses the knee in the flexed position.

The diagnosis is confirmed by clinical examination. In gross cases, the patient sitting on the edge of the exam table with the legs dangling and flexed at 90 degrees will first of all close the flexion gap, bringing the tibial component into contact with the posterior femoral condyles when they contract the quadriceps muscle. This vertical motion that precedes extension can be observed. Similarly, if the patient is supine, with the knee flexed to 90 degrees, the examiner may grasp the ankle and with a hand under the thigh, distract the flexion gap and then allow it to close. The travel and the clunk can be appreciated. The standard ‘posterior drawer’ test that is appropriate for the non-arthroplasty knee will only be useful for relatively non-constrained, cruciate dependent prostheses. It will not be useful for flexion instability in the posterior stabilised prosthesis. It is useful to perform this distraction maneuver in flexion, during the arthroplasty with trial components in place to confirm that the arthroplasty is stable in flexion. The common maneuver to assess the flexion gap, of internally and externally rotating the femur to detect medial lateral instability in flexion seems to be less accurate.

The patients at greatest risk for this complication are those presenting for arthroplasty with a fixed flexion contracture. If a measured resection technique is employed without consideration of correcting the tighter extension gap, when a (relatively thinner) poly insert is selected to achieve full extension, it will not be thick enough to stabilise the larger/normal flexion gap. Flexion instability should not be confused with so-called “mid-flexion” instability, which is a poorly defined and much more subtle, clinical entity that has been described in case reports of revision surgery and the cadaver laboratory. Although more conforming articular polyethylene inserts may resolve this problem, even if revision is performed to a more constrained component, the essence of the solution is revision arthroplasty to balance the flexion and extension gaps.

The concept under discussion is curious and central to our work: is patient dissatisfaction with modern TKA really a “growing problem”? Could it be, that as our technique and technology have improved function and durability, that surgical results have become worse????

A disappointing percentage of patients polled from a distance are less than fully satisfied with the results of their surgery. Why does this surprise us as surgeons?

This problem needs to be untangled. First, these studies ask patients blankly if they are satisfied with their surgery, generally and with respect to specific criteria (e.g. activities of daily living). Neither the patients nor their radiographs have been evaluated. Undoubtedly, some dissatisfied patients will have arthroplasties that would be assessed as less than perfect by a comprehensive evaluation that might include stability testing, range of motion and radiographs of patellar tracking, including CT examination for rotational positioning of components. Some will have suffered the recognised complications of surgery such as chronic regional pain syndrome and infections which, while treated, often yield poor results. Surgeons all too often abandon a systematic and comprehensive evaluation, almost dismissing patients who complain.

A second group will be disabled due to physical factors extrinsic to the arthroplasty: polyarthritis, deconditioning and medical comorbidities. Others suffer depression and are disappointed that life never improved after the arthroplasty.

Thirdly, another group will have knees that could not technically have been any better, but who are still dissatisfied with the result. Some had expectations that exceeded the capability of current technology to reproduce knee function. Their surgeons failed to convey the potential of arthroplasty to make things “normal” in a way that the patient could incorporate. Other patients may have submitted to surgery prematurely, before arthritis and knee dysfunction, had reached the point where arthroplasty represents an improvement.

The concept of a “growing problem”, has more to do with the disjunction between rapidly accelerating public expectations (fueled by modern medicine) and the more modest rate of progress in technology, technique and education. Happy patients tend to be satisfied and there are a great many factors that determine happiness.

Assessment depends on tools for measurement. Surgeons have struggled honestly to develop tools that could help assess which prostheses and techniques were superior, to make wise choices in developing techniques and implants. Many of the original clinical assessment tools have been challenged as invalid. Newer more comprehensive tools have been developed. The “evidence based” movement, and rejection of some clinical tools, represents a shift in power in clinical medicine that has “enabled payers, purchasers, and governmental authorities to use their financial clout to alter the practice of medicine.” (http://www.ahrq.gov/research/findings/evidence-based-reports/jhppl/rodwin.html)

This information is a call for practitioners to evaluate dissatisfied individuals compassionately and objectively and for investigators to evaluate the entire problem exhaustively. Skepticism is appropriate when this message is a glib pretext for commercialisation and/or for denigration of the role of arthroplasty in the lives of our patients. It is a call to improve, not abandon our craft.

“Expert opinion” is the lowest totem on the academic pole and yet, “evidence based” medicine does not always provide us answers for the particular, the unusual clinical problem. Well-controlled studies are precisely that: “well-controlled”. Life may be randomised, but falls short of being “well-controlled”.

The challenge and honor of moderating a panel of experienced and articulate colleagues is to bring out “how they think” and how they formulate a plan for complex cases. The panel members are not only experienced practitioners, but they are the authors of studies that shape our profession. What are the limits to the studies they have published? What insight can they provide us to help understand “level 1” data more astutely? What biases and assumptions support their methods? Nothing achieves that with greater clarity than presentation of complex cases to an accomplished panel.

Several ordinary clinical problems are presented to establish current practice, followed by the unexpected outcomes to illustrate how experts deal with adversity.

There is a renewed debate regarding the relative importance of (primarily varus-valgus) stability versus alignment in TKA. Some surgeons have posited that stability is of greater importance. Perhaps this is because unstable knees fail immediately whereas mal-aligned knees generally suffer late failure from wear, osteolysis and loosening. Or perhaps some surgeons find soft tissue techniques challenging. Clearly alignment and stability are both necessary for immediate function and long-term durability.

Ligament tensioners are as old as condylar knee arthroplasties. They first appeared when surgeons moved beyond hinged arthroplasties with a goal of melding anatomy and biomechanics- to re-establish stability and correct pathologic deformity. Early techniques stipulated that ligament releases should be performed first, before any bone cuts thus correcting deformity and restoring stability. Crude mechanical instruments were replaced by mechanical devices.

Acknowledging more exacting standards, our ability to hit the target of desired alignment and stability is limited unassisted. As more sophisticated devices have been introduced to help surgeons correct alignment we have not yet discovered the perfect mechanical, electronic, navigated or laser guided “tensioner”. We still struggle to divine the “best” alignment. The principle however endures, that integrating stability and alignment, if with nothing more than a “cognitive tensioner” is essential to optimal short and long term arthroplasty function.

“Expert opinion” is the lowest totem on the academic pole- and yet, “evidence based” medicine does not always provide us answers for the particular, the unusual clinical problem. Well-controlled studies are precisely that: “well controlled”. Life may be randomised, but falls short of being “well controlled”.

The challenge and honor of moderating a panel of experienced and articulate colleagues is to bring out “how they think” and how they formulate a plan for complex cases. The panel members are not only experienced practitioners, but they are the authors of studies that shape our profession. What are the limits to the studies they have published? What insight can they provide us to help understand “level 1” data more astutely? What biases and assumptions support their methods? Nothing achieves that with greater clarity than presentation of complex cases to an accomplished panel.

Several ordinary clinical problems are presented to establish current practice, followed by the unexpected outcomes to illustrate how experts deal with adversity.

The “keel” is the relatively short part of the undersurface of the tibial component that extends into the medullary canal. Most knee replacement systems have the capacity to attach modular stem extensions for enhanced intra-medullary fixation for revision.

Diaphyseal length, large diameter stems may also guide positioning of trial components and are ideal for accurate surgical technique, even if fully cemented stems are eventually implanted.

Smaller diameter non-modular stem extensions may be used for fully cemented fixation. They do not however guide component position very accurately and do not make sense for uncemented fixation. Revision surgery is different from primary surgery and enhanced fixation with some type of intramedullary fixation is highly appropriate, especially if constrained devices might be required.

Options for enhanced intramedullary fixation are: 1. Fully cemented metaphyseal or shorter stems; 2. Diaphyseal engaging press fit stems; and 3. Very short fully cemented stems with trabecular metal cone fixation.

Metaphyseal length press fit stems do not provide reliable fixation in revision TKA. Revision with primary components or constrained components without any stem extension is not advised.

The causes of pain after TKA can be local (intra or extra-articular) or referred from a remote source. Local intra-articular causes include prosthetic loosening, infection, aseptic synovitis (wear debris, hemarthrosis, instability, allergy), impingement (bone soft tissue or prosthetic), an un-resurfaced patella and stress fracture of bone or the prosthesis. Some surgeons think that isolated component mal-rotation can be a source of pain, but component mal-rotation is rarely present in the absence of other technical abnormalities.

Local extra-articular causes include pes anserine bursitis, saphenous neuroma/dysasthesias, post-tourniquet dysasthesias, complex regional pain syndrome and vascular claudication.

Referred pain is most often from an arthritic hip or radicular pain from a spinal source. Patients with fibromyalgia can have persistent pain following their knee arthroplasty and should be warned of this possibility.

Evaluation of the patient includes a history, physical exam, joint aspiration and plain radiographs. In selected patients, an anesthetic joint injection, bone scan, CT scan or MRI with metal subtraction may be helpful in the diagnosis. The joint aspiration should include a CBC and differential as well as an aerobic and anaerobic culture. Fungal and TB cultures are sometimes indicated.

Re-operation for pain of unknown etiology following TKA is unlikely to yield an excellent result and both surgeons and patients should be aware of this probability.