In a recent study, 54.5% of patients reporting to arthroplasty clinics in the US were obese. We performed a recent literature review to determine how obesity impacts outcomes in total hip and knee arthroplasty and what must be done to improve outcomes in the obese arthroplasty patient.

Specifically, obese patients have shown increased rates of infection, dislocation, need for revision, wound dehiscence, increased operative time and prolonged hospital stay. Additionally, obese TKA patients have been shown to have increased rates of aseptic loosening, thromboembolic events, wound complications, and cardiopulmonary events.

Worsening severity of obesity seems to correlate with worsening outcomes and super obesity (BMI>50) has been identified as an independent risk factor for complications. Patients with BMI>35 have shown to be 6.7 times more likely to develop infection after TKA. Patients with BMI>40 have a 3.35 times higher rate of revision for deep infection than those with BMI<35. The odds ratio for major complications increases dramatically beyond BMI>45.

How can we improve outcomes in the obese patient? Preoperative care for the obese patient involves nutritional counseling, incorporating weight loss methods, physical therapy, metabolic workup and diagnosis and management of frequent comorbid conditions (OSA, DM2, HTN, HLD, malnutrition, renal failure). Identifying and managing comorbidities is especially important given that some comorbidities such as malnutrition have been shown to be as strong or even stronger an independent risk factor for postoperative TJA complications than obesity. In some cases higher complications were seen which some authors attribute to bariatric patients remaining in a catabolic state after weight loss.  

We know that obesity and its associated comorbid conditions do have worse outcomes and increased complications in TJA patients. We also know that complications proportionately increase with increasing severity of obesity. The super-obese population is at the greatest risk of complication following TJA and preoperative screening and management is essential in reducing complications. Although weight loss is important, bariatric data has shown that it does not solve the problem of obesity in itself and the patient's metabolic state is likely a more important issue. Implant selection is important and strong consideration should be given to avoiding direct anterior approach in the THA obese patient. Understanding of obesity specific complications and treatment options is crucial for patient counseling and optimization to ensure successful treatment in obese TJA patients.

The development of more wear resistant biomaterials and better locking mechanisms for the polyethylene into the tibial base has significantly reduced polyethylene wear as a reason for revision TKA. Aseptic loosening is now the primary cause for revision TKA. Loosening can be caused by multifactorial operative issues: 1] patient selection, 2] implant alignment, 3] cementing technique. Furthermore, aseptic loosening occurs at a consistent rate over time. Increased cement penetration is important to counter bone resorption. Increasing penetration also improves cement mantle toughness leading to better mechanical integrity of the bone-cement interface and reduces bone-cement interface stress.

It is important to recognise that a cleaner and drier interface does improve bone-cement penetration. Techniques to improve the process include better cement formulations, drilling sclerotic bone, devices and implant features to increase pressurization, using negative pressure suction ports in the tibia. We have extensive experience with CarboJet, a method of CO₂ gas jet cleaning and drying. This experience was developed during 20 years of performing TKA with NO tourniquet. Schnetler et al found that the “use of a tourniquet in TKA causes a paradoxical increase in total blood loss”. So, NO tourniquet TKA is becoming the new paradigm for knee arthroplasty in reconstructive orthopaedics. Goldstein reported that pressurised carbon dioxide jet lavage resulted in a 35% increase in cement penetration depth when used vs. use of pulsatile saline lavage alone. Meneghini used this pressurised carbon dioxide system to study the influence of NO tourniquet use in TKA. He found a significant lowering of opioid consumption postoperatively.

Another important factor in increasing the cement interdigitation is the influence of lipids which significantly weakens the bond at the interfaces. If motion is allowed during cementation there is additional loss of penetration and therefore fixation. The pressurised carbon dioxide delivered by the CarboJet system actually pushes the lipid, fatty marrow up and out of the bone allowing it to be suctioned or lap dried from the interface surface. The NO tourniquet technique and the use of carbon dioxide jet gas delivery to improve the bone-cement interface in TKA will be demonstrated.

INTRODUCTION

Variability in placement of total shoulder arthroplasty (TSA) glenoid implants has led to the increased use of 3D CT preoperative planning software. Computer assisted surgery (CAS) offers the potential of improved accuracy in TSA while following a preoperative plan, as well as the flexibility for intraoperative adjustment during the procedure. This study compares the accuracy of implantation of reverse total shoulder arthroplasty (rTSA) glenoid implants using a CAS TSA system verses traditional non-navigated techniques in 30 cadaveric shoulders relative to a preoperative plan from 3D CT software.

Introduction & Aims

Over the last decade, sensor technology has proven its benefits in total knee arthroplasty, allowing the quantitative assessment of tension in the medial and lateral compartment of the tibiofemoral joint through the range of motion (VERASENSE, OrthoSensor Inc, FL, USA). In reversal total shoulder arthroplasty, it is well understood that stability is primarily controlled by the active and passive structures surrounding the articulating surfaces. At current, assessing the tension in these stabilizing structures remains however highly subjective and relies on the surgeons’ feel and experience. In an attempt to quantify this feel and address instability as a dominant cause for revision surgery, this paper introduces an intra-articular load sensor for reverse total shoulder arthroplasty (RTSA).

INTRODUCTION

Preoperative planning software for anatomic total shoulder arthroplasty (ATSA) allows surgeons to virtually perform a reconstruction based off 3D models generated from CT scans of the glenohumeral joint. The purpose of this study was to examine the distribution of chosen glenoid implant as a function of glenoid wear severity, and to evaluate the inter-surgeon variability of optimal glenoid component placement in ATSA.

INTRODUCTION

Preoperative planning software for reverse total shoulder arthroplasty (RTSA) allows surgeons to virtually perform a reconstruction based off 3D models generated from CT scans of the glenohumeral joint. While anatomical studies have defined the range of normal values for glenoid version and inclination, there is no clear consensus on glenoid component selection and position for RTSA. The purpose of this study was to examine the distribution of chosen glenoid implant as a function of glenoid wear severity, and to evaluate the inter-surgeon variability of optimal glenoid component placement in RTSA.

The development of more wear resistant biomaterials and better locking mechanisms for the polyethylene into the tibial base has significantly reduced polyethylene wear as a reason for revision TKA. Aseptic loosening is now the primary cause for revision TKA. Loosening can be caused by multifactorial operative issues: 1] patient selection, 2] implant alignment, 3] cementing technique. Furthermore, aseptic loosening occurs at a consistent rate over time. Increased cement penetration is important to counter bone resorption. Increasing penetration also improves cement mantle toughness leading to better mechanical integrity of the bone-cement interface and reduces bone-cement interface stress.

It is important to recognise that a cleaner and drier interface does improve bone-cement penetration. Techniques to improve the process include better cement formulations, drilling sclerotic bone, devices and implant features to increase pressurization, using negative pressure suction ports in the tibia. We have extensive experience with CarboJet, a method of CO2 gas jet cleaning and drying. This experience was developed during 20 years of performing TKA with NO tourniquet. Schnetler et al found that the “use of a tourniquet in TKA causes a paradoxical increase in total blood loss”. So, NO tourniquet TKA is becoming the new paradigm for knee arthroplasty in reconstructive orthopaedics. Goldstein reported that pressurised carbon dioxide jet lavage resulted in a 35% increase in cement penetration depth when used versus use of pulsatile saline lavage alone.

Another important factor in increasing the cement interdigitation is the influence of lipids which significantly weakens the bond at the interfaces. If motion is allowed during cementation there is additional loss of penetration and therefore fixation. The pressurised carbon dioxide delivered by the CarboJet system actually pushes the lipid, fatty marrow up and out of the bone allowing it to be suctioned or lap dried from the interface surface. The NO tourniquet technique and the use of carbon dioxide jet gas delivery to improve the bone-cement interface in TKA will be demonstrated.

Total knee arthroplasty (TKA) is one of the most common orthopaedic operations performed worldwide and it is largely successful in pain relief and functional recovery. However, when pain persists post-operatively the thorough evaluation must be instituted. Extra-articular causes of knee pain include; hip pathology, lumbar spine degenerative disease or radicular symptoms, focal neuropathy, vascular disease, and chronic regional pain syndrome. Intra-articular causes of knee pain: infection, crepitation/clunk, patella osteonecrosis, patella mal-tracking, soft tissue imbalance, malalignment, arthrofibrosis, component loosening, implant wear, ilio-tibial band irritation, and bursitis. Other causes of pain to rule out are component overhang with soft tissue irritation, recurrent hemarthrosis secondary to synovial impingement or entrapment, non-resurfaced patella, and metal sensitivity.

A careful history may reveal previous knee surgeries with delayed healing or prolonged drainage, chronology of sign and symptoms, co-morbid medical conditions, jewel or metal sensitivity.

Physical exam should help with specific signs in the operated knee. Targeted local anesthetic blocks are helpful and response to lumbar sympathetic blocks determines presence of CRPS.

Lab tests are important: ESR, CRP, WBC, aspiration with manual cell count and diff, leucocyte esterase dipstick, RA titers, metal derm patch testing, nuclear scans, CT best for rotational malalignment, and MARS MRI.

More recently patient satisfaction as an outcome measure has shown TKA results not satisfactory in 11- 18% of patients. A discordance of patient vs. surgeon satisfaction exists so the following factors may help improve this: correct patient selection, establishing and correlating surgeon-patient expectations, peri-operative optimization of patient co-morbidities to help avoid preventable complications, use of pre-operative and post-operative pathways. Satisfaction rates can best be improved by addressing the previous points with patients prior to TKA surgery.

The US obesity epidemic has transcended into the arthroplasty patient population and surgeons must assess whether obesity is a risk factor for poor outcomes in total joint arthroplasty (TJA) and determine how it should be managed in order to insure good clinical outcomes. In the United States, 34.9% of adults are currently obese (BMI > 30). In a recent study, 54.5% of patients reporting to arthroplasty clinics in the US were obese. We performed a recent literature review to determine how obesity impacts outcomes in total hip and knee arthroplasty and what must be done to improve outcomes in the obese arthroplasty patient.

We know that obesity and its associated comorbid conditions do have worse outcomes and increased complications in TJA patients. We also know that complications proportionately increase with increasing severity of obesity. The super-obese population is at the greatest risk of complication following TJA and pre-operative screening and management is essential in reducing complications. Although weight loss is important, our bariatric data has shown that it does not solve the problem of obesity in itself and the patient's metabolic state is likely a more important issue. Implant selection is important and strong consideration should be given to avoiding direct anterior approach in the THA obese patient. Understanding of obesity specific complications and treatment options is crucial for patient counseling and optimisation to ensure successful treatment in obese TJA patients.

TKA is one of the most common orthopaedic operations performed worldwide and it is largely successful in pain relief and functional recovery. However, when pain persists post-operatively the thorough evaluation must be instituted. Extra-articular causes of knee pain include; hip pathology, lumbar spine degenerative disease or radicular symptoms, focal neuropathy, vascular disease, and chronic regional pain syndrome. Intra-articular causes of knee pain: infection, crepitation/ clunk, patella osteonecrosis, patella mal-tracking, soft tissue imbalance, malalignment, arthrofibrosis, component loosening, implant wear, ilio-tibial band irritation, and bursitis. Other causes of pain to rule out are component overhang with soft tissue irritation, recurrent hemarthrosis secondary to synovial impingement or entrapment, non-resurfaced patella, and metal sensitivity.

A careful history may reveal previous knee surgeries with delayed healing or prolonged drainage, chronology of sign and symptoms, co-morbid medical conditions, jewel or metal sensitivity.

Physical exam should help with specific signs in the operated knee. Targeted local anesthetic blocks are helpful and response to lumbar sympathetic blocks determines presence of CRPS.

Lab tests are important: ESR, CRP, WBC, aspiration with manual cell count and diff, leukocyte esterase dipstick, RA titers, metal derm patch testing, nuclear scans, CT best for rotational malalignment,, and MARS MRI.

More recently patient satisfaction as an outcome measure has shown TKA results not satisfactory in 11 – 18% of patients. A discordance of patient vs. surgeon satisfaction exists so the following factors may help improve this: correct patient selection, establishing and correlating surgeon-patient expectations, peri-operative optimisation of patient comorbidities to help avoid preventable complications, use of pre- and post-operative pathways. Satisfaction rates can best be improved by addressing the previous points with patients prior to TKA surgery.

Functional restoration of patella kinematics is an essential component of TKA, whether the patella is replaced or not. This goal is accomplished by a multifactorial approach: establish proper component position and alignment, especially rotation; avoid IR of the femoral and ER of the tibial components; maintain correct joint line position; achieve symmetrical soft tissue balance.

Most modern TKA designs have an anatomic trochlear groove shape to enable midline tracking. Patella implants are better designed as well with three equilateral lugs for fixation and either dome or anatomic shape. The apex of the patella component should be aligned with the apex of the patella raphe which is more medial than lateral. This method leaves an island of exposed lateral patella facet which is managed with the “lateral slat technique” to be described. It is essentially an intraosseous lateral release. The early mobilization of modern TKA patients demands watertight closure to prevent soft tissue attenuation and late tracking issues.

When confronted with a patient with a laterally dislocated patella, implementation of the “lateral slat technique” should be done at the approach to obtain midline tracking. Such patients require a median parapatellar (MPP) approach and may need distal-lateral vastus medialis advancement (Insall procedure).

Adherence to the principles iterated herein will produce a happy patient with good patello-femoral kinematics and function.

As the American population ages and a trend toward performing total hip arthroplasty (THA) in younger patients continues, the number of Americans undergoing THA is projected to increase over time. The advent of the bundled payment system combined with the current medical utilization climate has placed considerable pressure on surgeons to produce excellent results with early functional recovery and short hospital stays. The US obesity epidemic has transcended into the arthroplasty patient population and surgeons must assess whether obesity is a risk factor for poor outcomes in THA and determine how it should be managed. We performed a recent literature review to determine how obesity impacts outcomes in total hip arthroplasty and what must be done to improve outcomes in the obese arthroplasty patient. Our goal is to answer 3 questions: does obesity increase the complication rate in THA, if obesity matters how obese is too obese, and what must be done to improve outcomes in the obese patient?

Ultimately, obesity has been shown to correlate with increased post-operative complications in THA. The arthroplasty surgeon must optimise the obese patient prior to surgery by identifying associated comorbidities and consider malnutrition screening with counseling. Notice should be taken of the degree of obesity as patients with BMI > 40 have demonstrated much higher complication rates. Strong consideration should be given to avoiding direct anterior approach in the obese patient. Healthy weight loss must be encouraged with appropriate patient counseling and treatment in order to achieve success with THA in obese patients.

The femur begins to bow anteriorly at the 200 mm level, but may bow earlier in smaller people. If the stem to be used is less than 200 mm, a straight stem can be used. If the stem is longer than 200 mm, it will perforate the anterior femoral cortex. I know this because I did this on a few occasions more than 20 years ago.

To use a long straight stem, there are two techniques. One can either do a diaphyseal osteotomy or one can do a Wagner split (extended trochanteric osteotomy). Both of these will put the knee in some degree of hyperextension, probably insignificant in the elderly, but it may be of significance in the young. In very young people, therefore, it may be preferable to use a bowed stem to avoid this degree of recurvatum.

There are two different concepts of loading. Diaphyseal osteotomy implies a proximal loading has been sought. The Wagner split ignores the proximal femur and seeks conical fixation in the diaphysis. There will be very little bone-bone contact between what remains of the attached femur and the detached anterior cortex so that it is important to ensure that the blood supply to the anterior cortex remains intact, preferably by using Wagner's technique, using a quarter-inch osteotome inserted through the vastus to crack the medial cortex. Current modularity is of two types. Distal modularity was attempted many years ago and was never successful.

Proximal modularity, as for example, the S-ROM stem, implies various sizes of sleeves fit onto the stem to get a proximal canal fill. In mid-stem modularity, the distal stem wedges into the cone. It has to be driven into where it jams and this can be somewhat unpredictable. For this reason, the solid Wagner stem has been replaced by the mid-stem modular. Once the distal femur is solidly embedded, the proximal body is then selected for height and version. The proximal body is unsupported in the mid-stem modular and initially, few fractures were noted at the taper junction. Cold rolling, shot peening and taper strengthening seem to have solved these problems.

There are a variety of types of osteotomy, which can be used for different deformities. With a mid-stem modular system, generally, all that needs to be done is a Wagner-type split and fixation is sought in the mid-diaphysis by conical reaming. No matter what stem is used, distal stability is necessary. This is achieved by flutes, which engage the endosteal cortex. The flutes alone must have sufficient rotational stability to overcome the service loads on the hip of 22 Nm.

I divide revision into three categories. In type one, the isthmus is intact, i.e. the bone below the lesser trochanter so that a primary stem can be used. In type two, the isthmus is damaged, i.e. the bone below the lesser trochanter, so a long revision stem is required. In a type three, there is more than 70 mm of missing proximal femur. The Wagner stem may be able to handle this on its own, but most other stems are better supported with a structural allograft cemented to the stem.

The reported long term results of mid-stem modular revision implants are good as in most, over 90% survivorship. The introduction of modularity appears to have overcome initial disadvantage of the Wagner stem, i.e. its unpredictability in terms of leg length.

Introduction

Humeral radiolucent lines after anatomic TSA (aTSA) have been well described; however, little clinical consequences have been attributed to them. The recent emergence of shorter humeral stems has demonstrated higher incidences of humeral radiolucencies than has been reported historically with standard length components. This large scale database analysis quantifies and compares the clinical outcomes of aTSAs with and without radiolucent humeral lines using one specific prosthesis to determine their impact on clinical outcomes.

INTRODUCTION

As computer navigated surgery continues to progress to the forefront of orthopedic care, the application of a navigated total shoulder arthroplasty has yet to appear. However, the accuracy of these systems is debated, as well as the dilemma of placing an accurate tool in an inaccurate hand. Often times a system's accuracy is claimed or validated based on postoperative imaging, but the true positioning is difficult to verify. In this study, a navigation system was used to preoperatively plan, guide, and implant surrogate shoulder glenoid implants and fiducials in nine cadaveric shoulders. A novel method to validate the position of these implants and accuracy of the system was performed using pre and post operative high resolution CT scans, in conjunction with barium sulfate impregnated PEEK surrogate implants.

Obtaining primary wound healing in total joint arthroplasty (TJA) is essential to a good result. Wound healing disturbances (WHD) can occur and the consequences can be devastating to the patient and to the surgeon. Determination of the host healing capacity can be useful in predicting complications. Cierney and Mader classified patients as Type A: no healing compromises and Type B: systemic or local healing compromise factors present. Local factors include traumatic arthritis with multiple previous incisions, extensive scarring, lymphodema, poor vascular perfusion, and excessive local adipose deposition. Systemic compromising factors include diabetes, rheumatic diseases, renal or liver disease, immunocompromise, steroids, smoking, and poor nutrition. Low serum albumin, total lymphocyte count, and low transferrin increase WHD. In high risk situations the surgeon should encourage positive patient choices such as smoking cessation and nutritional supplementation to modify healing responses. Use of tourniquet in obese patients also increases WHD.

Careful planning of incisions, particularly in patients with scarring or multiple previous operations, is productive. Around the knee the vascular viability is better in the medial flap. Thusly, use the most lateral previous incision, do minimal undermining, and handle tissue meticulously. We do all potentially complicated TKA's without tourniquet to enhance blood flow and tissue viability. The use of perioperative anticoagulation will increase wound problems.

If wound drainage or healing problems do occur, immediate action is required. Deep sepsis can be ruled out with a joint aspiration and cell count (less than 2500), differential (less than 60% polys), and negative culture and sensitivity. All hematomas should be evacuated and necrosis or dehiscence should be managed by debridement to obtain a live wound.

The major benefit of TKA with tourniquet is operating in a bloodless field. A possible secondary benefit is a better cement-bone interface for fixation.

The disadvantages of tourniquet use for TKA include multiple risk factors both local and systemic: Nerve damage, Altered hemodynamics with limb exsanguinations (15–20% increase in circulatory volume) and reactive hyperemia with tourniquet release (10% increase in limb size increasing soft tissue tension and secondary pain), Delay in recovery of muscle function, Increased risk of DVT with direct trauma to vessel walls and increased levels of thrombin-antithrombin complexes, A 5.3x greater risk for large venous emboli propagation and transesophageal echogenic particles, Vascular injury with higher risk in atherosclerotic, calcified arteries, Increase in wound healing disturbances, Obese patients TKA with tourniquet show impaired endothelial function and more DVTs.

Our initial experience with TKA without tourniquet was in high risk patients with previous DVT or PE, multiple scarring, or compromised cardiovascular status. We have used this method on all patients for the last 14 years. The protocol includes regional anesthesia, incision and approach made with 90-degree knee flexion, meticulous hemostasis, jet lavage and filtered carbon dioxide delivered to dry and prepare bone beds for cementation, application of topical tranexamic acid and routine closure. We have encountered no differences in blood loss or transfusion rates, cement penetration/ fixation, less postoperative pain, faster straight leg raise and knee flexion gains, and fewer wound healing disturbances. We recommend TKA sans tourniquet. Let it bleed!

In the USA, 34.9% of adults are currently obese (BMI > 30). Growth in total knee arthroplasty (TKA) is outpacing growth in total hip arthroplasty (THA) largely due to a differential utilization of TKA in overweight patients in the USA. In a recent study, 54.5% of patients reporting to arthroplasty clinics in the USA were obese. From 2006–2010, 61.2% of primary unilateral TKA patients in the USA ACS-NSQIP database were obese. Arthroplasty surgeons are directly affected by the obesity epidemic and need to understand how to safely offer a range of peri-operative care for these patients in order to insure good clinical outcomes.

Pre-operative care for the obese patient involves nutritional counseling, weight loss methods, consideration for bariatric surgery, physical therapy, metabolic workup, and diagnosis and management of frequent comorbid conditions (OSA, DM2, HTN, HLD). Obese patients must also be counseled on their increased risk of complications following TKA.

In the operating room, several steps can be taken to insure success when performing TKA on obese patients. We recommend performing TKA without the use of a tourniquet in order to prevent fat necrosis and increased pain. The incision is made in 90 degrees of knee flexion, atypically midline proximally and curved distally to the midpoint between the tubercle and the medial edge of the tibia. Care is used to minimise the creation of dead space, and the approach to the knee is an extensile medial parapatellar incision. Closure is in multiple layers. The use of negative pressure dressing following surgery can minimise the early wound drainage that is frequently seen after TKA in obese patients.

Post-operative care of the obese patient following TKA involves several unique considerations. Chronic pain and obesity are frequent comorbid conditions and post-operative pain control regimens need to be tailored. Although the physical therapy regimen does not differ in obese patients, obese patients are more likely to be discharged to a rehabilitation facility.

Obese patients have a higher rate of all complications compared to healthy weight. All infection and deep infection increased in obese patients in large meta-analysis. Patients with BMI > 35 are 6.7 times more likely to develop infection after TKA. Patients with BMI > 40 have a 3.35 times higher rate of revision for deep infection than those with BMI < 35. The odds ratio for major complications increases dramatically beyond BMI > 45.

Although there are a few studies that have demonstrated worse clinical outcome in obese patients following TKA, most studies show no difference in clinical outcomes at short- or long-term follow-up. The arthroplasty surgeon must optimise the obese patient prior to surgery, use intra-operative techniques to maximise success, and anticipate potential problems in the post-operative course in order to achieve success with TKA in obese patients.

Functional restoration of patella kinematics is an essential component of TKA, whether the patella is replaced or not. This goal is accomplished by a multifactorial approach: establish proper component position and alignment, especially rotation, avoid IR of the femoral and ER of the tibial components, maintain correct joint line position, achieve symmetrical soft tissue balance

Most modern TKA designs have an anatomic trochlear groove shape to enable midline tracking. Patella implants are better designed as well with three equilateral lugs for fixation and either dome or anatomic shape. The apex of the patella component should be aligned with the apex of the patella raphe which is more medial than lateral. This method leaves an island of exposed lateral patella facet which is managed with the “lateral slat technique” to be described. It is essentially an intraosseous lateral release. The early mobilization of modern TKA patients demands watertight closure to prevent soft tissue attenuation and late tracking issues.

When confronted with a patient with a laterally dislocated patella, implementation of the “lateral slat technique” should be done at the approach to obtain midline tracking. Such patients require a median parapatellar (MPP) approach and may need distal-lateral vastus medialis advancement (Insall procedure).

Adherence to the principles iterated herein will produce a happy patient with good patello-femoral kinematics and function.

Persistent post-surgical pain (PPSP) remains a problem after knee replacement with some studies reporting up to 20% incidence. Pain is usually felt by those who do not operate to be a monolithic entity. All orthopaedic surgeons know that this is not the case. At its most basic level, pain can be divided into two categories, mechanical and non-mechanical.

Mechanical pain is like the pain of a fresh fracture. If the patient does not move, the pain is less. This type of pain is relieved by opiates. Mechanical pain is seen following knee replacement, but is becoming less frequent. It is caused by a combination of malrotations and maltranslations, often minor, which on their own would not produce problems. The combination of them, however, may produce a knee in which there is overload of the extensor mechanism or of the medial stabilizing structures. If these minor mechanical problems can be identified, then corrective surgery will help.

Non-mechanical pain is present on a constant basis. It is not significantly worsened by activities. Opiates may make the patient feel better, but they do not change the essential nature of the pain. Non-mechanical pain falls into three broad groups, infection, neuropathic and perceived pain. Infection pain is usually relieved by opiates. Since some of this pain is probably due to pressure, its inclusion in the non-mechanical pain group is questionable, but it is better left there so that the surgeon always considers it. Low grade chronic infection can be extremely difficult to diagnose. Loosening of noncemented knee components is so rare that when it is noted radiologically, infection should be very high on the list of suspicions. The name neuropathic pain suggests that we know much more about it than we do in reality. Causalgia or CRPS-type two is rare following knee replacement. CRPS-type one or reflex sympathetic dystrophy probably does exist, but it is probably over-diagnosed. The optimum treatment I have found is lumbar sympathetic blocks. Lyrica, Gabapentin and Cymbalta may also help. Perceived pain is the largest group. It does not matter what you tell the patient, some believe a new knee should be like a new car, i.e. you step into it and drive away. The fact that they have to work to make it work is horrifying. Perceived pain is widespread. The classic treatise, Dr. Ian McNabb's book “Backache”, should be studied by all who wish to understand pain complaints.

Any experienced knee surgeon will have his list of red flags or caveats. I will list only a few. If the patient comes in with a form asking for a disability pension on the first visit. If the patient's mother answers the questions. If the patient comes in taking massive doses of opiates. If the patient is referred to you by a surgeon who does more knee replacements than you do.

There are other issues such as good old fibromyalgia, which appears to have gone the way of the dodo. It has been replaced by something equally silly called central sensitization. The theory of central sensitization is that if one has pain somewhere or other for three months or six months or whatever, there are going to be changes in the brain and spinal cord. It then does not matter what happens to the original pain, i.e. whether or not it goes away, the pain will persist because of the changes in the brain, hence, the title of the pain in the brain syndrome. If this theory was correct, we might as well all go home because we have all been wasting our time for the last 30 years because none of our patients would get any better. After all, all of our patients have had pain for a lot longer than three months, many of them have been involved in trauma and sometimes, compensation is at issue. The pain in the brain theory, therefore, sounds about as realistic as the flat earth society or the treatment of Galileo.