The patient's age frequently influences the reason that he or she seeks medical attention for evaluation of a knee complaint. Younger patients' complaints focus on pain and stability, while older patients' complaints are primarily pain and impaired function. Mechanical failure of the knee joint can result from meniscal tears, ligamentous injuries, and patellofemoral syndromes. Pain may result from any of these problems, as well as from inflammatory conditions, degenerative arthritis, and osteonecrosis. A careful history and physical examination, with ancillary studies when indicated, usually provide the clinician with a diagnosis and a treatment plan appropriate for the disease process.

The knee depends on its ligamentous structures for stability. The location of the attachments of the ligaments stabilize the knee in sagittal, rotational, and axial planes. The medial and lateral meniscus aid in stabilizing the knee in a rotational plane and function as secondary restraints in the sagittal plane. As the knee flexes and extends, there is present in terminal extension tibial external rotation. In addition, there is a translational posterior motion of the femur on the tibia as flexion begins and after 30⁰ of flexion. The relationship between the two articular surfaces remains static in the translational plane.

Extension of the knee is performed by the quadriceps muscle. The four muscles merge into a common tendon and insert into the patella. Extensions of the central part of this common tendon are the patellar tendon, which inserts into the tibial tubercle. Flexion of the knee is performed primarily by the semimembranous, semitendinous, and biceps femoris muscles and secondarily by the gastrocnemius and popliteus muscles.

The femoral nerve innervates the quadriceps muscle. It is formed by the posterior rami of L2, L3, and L4 spinal nerves. After the nerve leaves the femoral triangle, it becomes the saphenous nerve, which is a sensory nerve, and descends the leg with the greater saphenous vein to give off intrapatellar branches to the knee.

The obturator nerve is formed by the anterior rami of L2, L3, and L4. It innervates the adductors of the thigh; in addition it supplies the capsule of the knee, entering the joint with the middle geniculate artery.

The sciatic nerve is formed by the anterior rami of L4, L5, S1, S2, and S3. It divides in the upper part of the popliteal fossa into the common peroneal and tibial nerve. The tibial component of the nerve innervates the semimembranous, semitendinous, and long head of the biceps femoris. Innervation of the knee joint itself is by branches of the femoral and obturator nerves and by geniculate branches of the peroneal and tibial nerves.

The popliteal artery leaves Hunter's canal, crosses through the popliteal fossa, and divides into the anterior and posterior tibial arteries. Prior to its division, the artery gives off five articular branches and multiple muscular branches. The anastomosis around the knee is formed by the superior medial and lateral geniculate arteries, the inferior medial and lateral geniculate arteries, and the middle geniculate arteries from the popliteal artery, descending branch of the lateral circumflex artery, and the descending geniculate artery from the femoral artery.

Beyond the general anatomy of the knee in the reconstructive sense of major importance is the alignment of the lower extremity. Axial alignment is of major importance in the performance of knee arthroplasty and osteotomies.

Normal alignment has been evaluated in several anthropometric studies. It is accepted by most that in stance the knees are closer to the midline than the hips and the ankles are even closer to the midline than the knees. A line drawn from the centre of the femoral head to the centre of the ankle is the mechanical axis of the extremity and is approximately 3⁰ varus. The anatomical axis of the lower extremity is determined by the intersection of the anatomical axis of the femur which is valgus and the axis of the tibia. The anatomical axis is within a range of 5 to 9⁰ of valgus.

Normal alignment would imply that, if an individual has no abnormalities of the cartilage, the joint can be loaded in stance and gait so that forces are evenly distributed throughout the knee.

Alignment is an important consideration for the surgeon. Alteration in the alignment beyond the norm can accelerate cartilage deformation, and wear, and re-establishment of a more favourable alignment may improve the function of the knee.

The ideal alignment in total knee replacement is important to the longevity of the implant. If the implant can be loaded "favourably" with optimal implant stability and design there is the potential for a durable arthroplasty.

The adult patient with knee pain can be of any age. The clinical history of the patient with knee pain and dysfunction is important. A history of injury should be carefully explored as intra-articular fractures either involving the distal femur, proximal tibia, or patella can lead to post-traumatic arthritis with either a significant chondral injury or postfracture malalignment (Fig. 1) 2468. Anterior cruciate ligament injuries after initial recovery from the injury can be associated with minimal pain and minimal instability, yet with such chronic anterolateral instability as to enhance the development of meniscal tears and subsequent degenerative disease.

Patellofemoral syndromes are common and associated with varying degrees of knee dysfunction. Isolated degenerative arthritis involving the patellofemoral joint, although not common, is extremely disabling. Articular injury to the patella occurs as a result of a chronic malalignment syndrome of the patellofemoral joint or trauma with or without fracture of the patella.

From the beginning, the physician should be open to an extensive differential diagnosis and evaluation of the patient with knee pain. It is especially important as a surgeon to avoid the trap of limiting diagnostic possibilities and arriving at a premature conclusion as to causal relationship. A knee problem can be differentiated by the clinician as either a monarticular disease or manifestation of systemic disease. Familiarity with these patterns is important for a thorough evaluation. Pathological processes involving the hip joint and the lumbosacral spine not uncommonly produce referred pain to the knee. Synovitis of the knee with other joint involvement is likely to be associated with a rheumatic disorder or a systemic disease. A painful or swollen knee, as a monarticular complaint, may be the manifestations of infection, trauma, or gout and pseudogout.

Ultimately, an objective history is a means of assessing disability and a reasonable measure of the patient's needs and response to a given treatment.

The examination of the knee begins with inspection of the joint. Asymmetry between the two extremities is important to note and differentiation should be made from a knee effusion and enlargement from synovial capsular thickening. Alignment may be more clearly assessed on the basis of radiographs but axial, sagittal, and coronal alignment can be evaluated by physical examination with a patient, supine, standing, sitting, and in gait. An examination of the patella, tibial tubercle, and malleoli are helpful in assessing torsional abnormalities. Observation of stance and gait are important in evaluation of the degenerative knee.

Malalignment and angular thrust in gait, subtle at times, are objective measures of the pathological process present. The active and passive range of motion are noted at the time of examination. The normal arc of flexion (−5 to 135⁰) is frequently altered in the diseased knee. The location of pain can sometimes be isolated but not uncommonly is diffuse. The patella is easily palpated. In most people both the medial and lateral compartments, at least anteriorly, can be palpated. The superficial location of the knee allows assessment of the articular cartilage, presence of osteophyte, effusion, and capsular thickening. The articular cartilage of the patella is most easily evaluated with the knee in approximately 30⁰ of flexion. Side-to-side motion of the patella within the femoral trochlea with a moderate degree of pressure may produce a grinding sensation (grind test), suggesting pathology of articular cartilage. Lateral displacement of the patella with moderate pressure may produce a quadriceps contraction (apprehension test), a provocative test for patella instability.

Varus and valgus testing of the knee in extension, in 30⁰, and in 90⁰ of flexion are important in evaluating ligament stability. Examination of the ipsilateral hip, ankle, and foot are important and results influence treatment of knee problems.

Radiographic examination of the knee is an objective means of assessment of the joint, articulation, soft tissue, and alignment. The basic evaluation of the knee must include anterior/posterior, lateral, tunnel, and patellofemoral views.

Because the anterior/posterior view is influenced by weight bearing, an anterior/posterior standing view is not necessarily an accurate study if the extremity is too painful to bear weight (Fig. 2) 2469. A supine anterior/posterior stress view can confirm clinical suspicion of unicompartmental articular loss as well as ligament stability. A useful adjunct to the anterior/posterior view is the flexion weight-bearing radiograph. This radiograph is taken with a posterior/anterior view with the patient's knee in 30 to 40⁰ of flexion and the X-ray beam at 80⁰ to the long axis of the tibia. The flexion weight-bearing radiograph has a greater sensitivity to articular cartilage loss especially in the areas subject to early degenerative loss.

Tunnel views of the knee are invaluable in evaluation of the tibial plateau and posterior femoral condyles. Osteochondritis dissecans and osteonecrosis of the femoral condyles are observed more clearly in this view. The Merchant or Lauren views have limitations but are useful in axial evaluation of the patellofemoral joint (Fig. 3) 2470.

Pathological changes on plain radiographs can demonstrate effusions, joint space narrowing, subchondral sclerosis, osteophyte formation, subchondral cysts, loose bodies, cortical erosions, and deformity. Neoplastic processes, both benign and malignant, have a predilection for occurring about the knee; therefore, changes in the bony architecture should not be ignored.

Long-leg standing films are used for evaluation and planning of reconstructive surgery in a patient with a degenerative knee. Achieving proper knee alignment is paramount in knee arthroplasty and osteotomy surgery. Although disagreement may exist in many aspects of both types of surgery, concepts of idealized alignment have validity based on clinical studies. Standing anterior/posterior on a three-foot cassette is ideal for evaluation of the axial alignment. Inherent problems exist with this study. Increasing internal rotation of the knee will accentuate the degree of valgus and external rotation of the knee will accentuate the degree of varus. It is helpful for the surgeon to be present when this study is being performed.

In stance, because the ankles are closer to the midline, this angle in relationship to the vertical axis is one of varus (between 2 and 3⁰). The anatomical axis is the tibial femoral angle and could be measured directly from a radiograph by the intersection of lines drawn through the shafts of the tibia and femur. This angle is variable as well, with a range of normal between 5 and 9⁰ of valgus. The tibial - femoral angle is dependent on the geometry of the femur because the hip, shaft, and knee axes are the result of the inter-relationship of the length of the femur and the length, angle, and rotation of the femoral neck. Joint line position is dependent on the position of the lower extremity. Influenced by abduction or adduction of the hip, variations could be expected to exist from the normal to the pathological condition. Thigh girth, ipsilateral joint disease, and an ageing broad based gait with secondary abduction of the hip will place the joint line in a secondary valgus position.

Interpretation of radiographs of a prosthetic knee should take into account its design and type of fixation. Axial and sagittal alignment are adequately assessed where coronal alignment, no less important, may be difficult on plain radiographs. Depending on fixation, an interface may or may not be visualized. In a cemented implant, a normal lucency less than 2 mm occurs at the bone - cement interface. Assessment of the implant requires serial radiographs accurately to evaluate an implant for subsidence and loosening. Failure of implant fixation may be both an aseptic or septic process and plain radiographs will not separate the two (Fig. 4) 2471. Fracture and dislocation of the components can occur in the postoperative period.

Radionuclear imaging of the knee is a reasonable adjunct to plain radiographs of the knee. Technetium-99m phosphate bone scans are helpful in the diagnosis of osteonecrosis, especially when plain radiographs have not yet demonstrated a lesion. The diagnosis of an infectious process is more accurate using either indium or gallium compared with technetium scanning but should not be relied upon solely for diagnosis (Figs. 5, 6) 2472,2473.

Arthrography continues to be useful in combination with aspiration for evaluation of a joint prosthesis. More accurate information using this technique can be gained with radiological subtraction studies. With the advent and availability of magnetic resonance imaging, arthrography has otherwise become an outmoded means of evaluation of the knee. Magnetic resonance imaging is the primary non-surgical imaging modality of the knee. Accuracy of MRI examinations range from 64 to 95 per cent for the medial meniscus, and from 83 to 94 per cent for the lateral meniscus. Both computerized axial tomography and magnetic resonance imaging are in the evaluation of the patellofemoral joint (Fig. 7) 2474.

Beyond the mechanical problems of the knee secondary to meniscal disease and loose bodies, the adult without a significant history of trauma and knee pain will either have an inflammatory or degenerative process of the knee. Different stages of the disease process, the patient's age, and postoperative expectation for function and pain relief influence the ultimate decision for treatment. Basic management of all patients with a painful knee from arthritic conditions should include non-steroidal anti-inflammatory medication, orthotics when indicated, rest, localized corticosteroid injections, and weight loss. The response to non-operative treatment is variable, but many patients experience some improvement in their pain and function ability.

Debate exists as to the aetiology of osteoarthritis of the knee. Several mechanisms initiating cartilage destruction are known, but ultimately destruction of the matrix supersedes the ability of chondrocytes to repair a local defect. In the knee, a malunion of the tibia or femur after fracture with alteration in alignment and pathological loading of the joint will, in most cases, progress to osteoarthritis with time.

When primary or secondary osteoarthritis exists, an underlying process of matrix destruction occurs as load is in excess of the physiological limit of the cartilage, and deformation occurs. A self-perpetuating cycle of destruction continues as the force generated from loading the diseased knee produces asymmetric wear of cartilage and subsequent bone loss. This loss of cartilage and bone increases the deformity and the extent of malalignment. Unfortunately, this process increases the force and deformation of the joint surface and secondary asymmetric loading. In the valgus knee, patients can compensate this by alterations in their gait better than patients with varus alignment.

In idiopathic spontaneous osteonecrosis, the typical patients are women over the age of 60. The aetiology of this disorder is unknown. Diagnosis can be confirmed by a positive bone scan with focal uptake in the condyle. MRI is helpful in defining osteonecrosis of the knee, but the T&sub1; weighted image not uncommonly exaggerates the apparent size of the lesion generated on plain radiographs. Stages of osteonecrosis of the knee have been recognized to define the sequence of progression of this pathological process. In stage I disease, radiographs are normal and the bone scan is positive. Spontaneous resolution is possible if the disease does not progress beyond this stage. As the disease progresses to stage II, plain radiographs demonstrate only slight flattening of the condyle in association with a positive bone scan. If the size of the lesion remains small, symptoms frequently resolve. In later stages, radiographs demonstrate an area of lucency surrounded with sclerotic bone. Progression to stage V with joint space narrowing is the endpoint of the disease process (Figs. 8, 9) 2475,2476.

Osteonecrosis of the femoral condyle produces a segment of necrotic bone in the weight-bearing portion of the condyle which if progressive, causes subchondral fracture and collapse.

Patients usually have intense localized pain, and the clinical progression of the disease is highly dependent on the size of the lesion. Lesions that occupy an area less than 3.5 cm in diameter frequently are asymptomatic within a year.

The treatment of osteonecrosis is initially conservative until the size of the lesion is elucidated. When degenerative changes develop, surgical treatment is considered. Prosthetic replacement is the recommended treatment in the older age groups and tibial osteotomy, with or without bone grafting, is recommended in the younger age groups.

Arthroscopy is a widely accepted modality for treatment of disorders of the knee. In selected patients, arthroscopy is a valuable tool in the treatment of the arthritic knee. While realizing that the surgeon cannot manage all intra-articular disease of the knee, there are definite advantages to this procedure. The evaluation of intra-articular pathology is accurate, and operative procedures have a low complication rate with rapid return to full activity. The knee joint should always be completely evaluated. Therapeutic lavage improves 82 per cent of patients at 14 months and 40 per cent at 3 years. Partial meniscectomy in patients with advanced grades of degenerative articular cartilage show initial improvement with poor long-term results. Patients with mechanical symptoms, such as locking, that have meniscal tears benefit most from arthroscopic surgery; up to 80 per cent of these patients show improvement at 2 years. Attempts should be made always to preserve as much as possible of the meniscus. Loose bodies trapped in the joint or intercondylar notch can also cause mechanical symptoms and are generally easy to remove arthroscopically. In the degenerated knee, without true mechanical problems, procedures such as synovectomy and debridement have limited success, with less than 50 per cent of the patients demonstrating improvement for 5 years.

Arthroscopic synovectomy through multiple portals and using a motorized synovial resector in patients with either rheumatoid arthritis or haemophilia has a lower morbidity than open procedures. Fewer episodes of bleeding can be expected in the haemophiliac, but loss of motion is still a problem that can be diminished by the use of postoperative constant passive motion devices and adequate analgesia. Although radiographic progression of the disease is not changed, relief can be expected in both groups for as much as 70 per cent of patients at 7 years.

Synovial proliferative disorders are suitable for synovectomy. Included in this group are rheumatoid arthritis, pigmented villonodular synovitis, haemophilia, and synovial chondromatosis. Arthroscopic synovectomy has generally replaced open synovectomy in the rheumatoid and haemophiliac patient because of its reduced morbidity and ease of access to the entire knee joint. Indications for synovectomy in the rheumatoid knee would be failure of medical management with a persistent synovitis and minimal radiographic changes. The indication for synovectomy in the haemophiliac knee is recurrent, frequent haemathrosis, despite adequate haemostatic therapy, with a presence of a synovitis and minimal radiographic changes.

Open synovectomy is appropriate for pigmented villonodular synovitis, with technical emphasis on the completeness of synovectomy to reduce recurrence. In rheumatoid arthritis, laboratory evaluation of active enzymes of the abnormal joint discloses a return to the preoperative level 18 months later.

In considering a patient for osteotomy, several considerations must be made. Generally, the patient is younger, active, and the disease is confined to one compartment. Significant loads across the knee are accentuated by malalignment. Calculated static loads are inaccurate in defining stresses in the diseased knee. Separate dynamic studies by Harrington and Morrison have shown that the medial compartment can bear the majority of load even with valgus alignment. The goal of osteotomy is correcting the mechanical axis and decreasing loads in the diseased compartment of the knee.

Proximal tibial osteotomy may be performed for both varus and valgus deformities. The most common osteotomy performed is a valgus osteotomy proximal to the tibial tubercle for varus deformity. The advantages of performing an osteotomy proximal to the tibial tubercle are that the bone is cancellous and will heal more rapidly, the contractual forces of the quadriceps are compressive to the site of osteotomy, and, finally, the site of osteotomy is closer to the deformity.

A variety of guides are available. The use of intraoperative radiographs are prudent to improve reproducible postoperative alignment and to avoid complications. Different techniques are used for fixation; these include postoperative immobilization in a cylinder cast, staples, and contemporary fracture fixation techniques. Advantages of rigid fixation are the decreased necessity for postoperative immobilization and the shorter postoperative recovery. Disadvantages are increased surgical exposure, and increased difficulty in removing the devices if total knee replacement is required.

Surgical exposure of the proximal tibia for tibial osteotomy should take into consideration the future possibilities of additional procedures, especially total knee arthroplasty, which is usually performed through a midline incision. A slightly longer near-midline incision can be used for exposure of the proximal lateral tibia taking this into consideration. Depending on the surgeon's preference, other incisions can be considered without compromise of skin for future surgery. Either a transverse incision made laterally 2 cm below the joint line, or a longitudinal incision made slightly anterior to the fibula and continued proximally parallel to the thigh have been described for proximal tibial osteotomy.

The ideal patient for a proximal tibial osteotomy should be the younger individual who may be heavier than his ideal weight, under the age of 60, and when other conservative measures have failed. Range of motion is important and a flexion contracture greater than 15⁰, or flexion less than 90⁰ is less than ideal for the knee for intended osteotomy. Lateral subluxation is a relative contraindication to osteotomy. If the varus deformity is greater than 15⁰ a barrel vault type of osteotomy as described by Maquet should be necessary for correction.

Preoperative planning is germane to all osteotomies for the correction of tibial - femoral alignment or mechanical axis. Three-foot long-leg films are ideal for making computations for intraoperative surgical correction. These films may require the presence of the surgeon to assure their accuracy as variations in internal and external rotation may respectively accentuate valgus and varus deformity. In the varus knee, correction to 9 to 10⁰ of anatomic valgus is recommended—either that or a mechanical axis with 2 to 4⁰ of valgus beyond a neutral mechanical axis. In the valgus knee, correction to a neutral mechanical axis plus 4⁰, or an anatomic axis of 0⁰, is felt to be ideal. Slight over-correction is superior to under-correction, especially in the correction of the varus knee (Figs. 10, 11) 2477,2478.

Complications of the procedure are usually technical. The proximal fragment should be 2 cm below the joint line and parallel to the joint to prevent fractures into the joint and non-union. Under-correction, over-correction, and recurrence of deformity are not uncommon findings in the postoperative course. Peroneal nerve palsy, non-union, infections, deep vein thrombosis, and compartment syndrome are all complications of this procedure.

The results of valgus osteotomy can be misleading. The results may be excellent in 80 to 90 per cent of patients at 5 years but deterioration in satisfactory function occurs by 10 years. Slight over-correction of the mechanical axis is associated with better long-term results. Patients with high adduction moments have been identified as at risk for early recurrence of the varus deformity and an unfavourable long-term response to this procedure. Potential compromise of subsequent arthroplasty is a consideration for the older patient and with low failure rates reported in total knee arthroplasty, a more prudent choice may not be osteotomy even for those patients with unicompartmental disease. Satisfactory results of total knee arthroplasty after osteotomy in the majority of patients is comparable to those patients having only an index arthroplasty. The number of excellent results is lower and the procedure can be technically more difficult.

Varus osteotomy may be performed on the proximal tibia or distal femur. Indications for varus osteotomy on the tibia are limited to those deformities less than 12⁰. The joint line will be altered and tilted medially after varus osteotomy of the tibia with a tendency for subluxation of the knee. An additional disadvantage of performing the varus osteotomy through the proximal tibia is a relaxation effect on the medial collateral ligament which requires plication to avoid medial laxity.

Supracondylar varus osteotomy of the distal femur (Figs. 12, 13) 2479,2480 to an axial axis of 0⁰ may be performed with either a medial or lateral closing wedge and stabilization with an AO-ASIF 90⁰ osteotomy plate anticipating satisfactory results in 90 per cent of the patients. The complication rate is similar to that of proximal tibial osteotomy.

The major indication for an operative resurfacing procedure of the knee, either hemiarthroplasty, unicompartmental arthroplasty, arthroplasty, or total knee arthroplasty, is disabling pain. The most conservative of these procedures is the hemiarthroplasty (Figs. 14, 15) 2481,2482. Indications for this procedure are disease isolated to one compartment, passively corrected angular deformity, and a young patient with post-traumatic arthritis or obesity. Results are not always predictable; the rate of revision is 15 to 20 per cent at 8 years.

Unicompartmental replacement is an excellent procedure in the well selected patient. Ideally, the patient should be sedentary, not overweight, and have a minimal deformity (angulation less than 20⁰), with non-inflammatory arthritis being restricted to one compartment of the knee. Although patients with osteoarthritis can manifest inflammatory characteristics in their disease, the initiating event to the pathological process of osteoarthritis is abnormal loading of the articular cartilage beyond its yield point with deformation and loss of matrix. An inflammatory response can ensue as a result of degradative enzymes released by cellular elements of the knee. This distinction should be made from knees with inflammatory or crystalline arthropathy as unicompartmental arthroplasty performed in these conditions will fail with the presence of remaining articular cartilage subject to an ongoing pathological process.

The McKeever hemiarthroplasty is used without cement. Unicompartmental replacement is available in a cemented or uncemented design with experience limited in the uncemented designs. The initial Brigham unicompartmental replacement demonstrated good to excellent results in approximately 90 per cent of patients with a failure rate of only 1 per cent per year. No other series with follow-up greater than 5 years has duplicated these results. Marmor in an 11-year follow-up had results of 47 per cent satisfactory and 26 per cent failures. Additional reported series of unicompartmental replacements in the literature are available with wide-ranging results. Individual surgeons experienced in unicompartmental replacement continue to be enthusiastic about the results of the procedure. Failures in the past could usually be related to errors in surgical technique, patient selection, or components design. With this knowledge gained, continued use of unicondylar arthroplasty is favourable in the well selected patient (Fig. 16) 2483.

The advantages of unicompartmental arthroplasty over total knee arthroplasty is preservation of bone, the cruciate ligaments, and the patellofemoral articulation. Patients recover from the surgery rapidly and with preservation of anatomy, proprioception, and kinematics. Compared with recovery after osteotomy, recovery after arthroplasty is shorter. Full weight-bearing and functional motion are present within a month after surgery. The short-term complication rate is much less after a unicompartmental arthroplasty, compared with a total knee arthroplasty. If failure occurs, another osteotomy may be performed readily without undue technical difficulty. Failure of a unicompartmental arthroplasty is caused by aseptic loosening of the prosthesis, tibial subluxation, patellar impingement on the femoral component, component breakage, and progression of disease in other compartments of the knee.

For the patient with disabling bicompartment or tricompartment arthritis, total knee arthroplasty, with improved design, instrumentation, and technique, has become a predictable procedure with satisfactory long-term results. Controversies exist in several aspects of the surgery, but it is agreed that ideal postoperative alignment and proper soft tissue management are paramount to the success of total knee arthroplasty.

Optimal goals for postoperative axial alignment are the mechanical axis which passes through the centre of the knee and tibial femoral angle between 5 and 9⁰ of valgus. Sagittal alignment on the femur should be anatomical (plus or minus 2⁰) and on the tibia, anatomic or a posterior tilt is ideal.

Instrument systems primarily depend on an intramedullary femoral guide and extramedullary tibial guide for reproducible component position. There have been advocates of extramedullary femoral guides, but accuracy is less using either the femoral head or palpable shaft as a guide. Intramedullary tibial guides are attractive but extramedullary tibial guides have documented accuracy and are used predominantly.

Fixation is controversial and long-term results with uncemented knees are not available. The gold standard for comparing results is the cemented total condylar design. Satisfactory results are present in 90 per cent of the patients at 10 years follow-up. A comparable group of patients, with a posterior cruciate retaining implant, had 94.6 per cent good results at 10 years.

With the advent of uncemented and modular designs, new problems have been created. Initial problems quickly appeared with the patella component and failure occurred from rapid wear of the polyethylene, with subsequent fracture of the component and disassociation of the polyethylene from its metal backing. Patients would develop pain and frequently a severe synovial metallosis prior to revision. These events have led to a majority of surgeons using a non-metal backed patella component. The uncemented designs continue to make metal-backed patella components available. Modular design of the tibial components has optimized intraoperative decision making to allow optimal coverage of the proximal tibia and finalization of stability testing.

Bone defects encountered at the time of arthroplasty may be reconstructed with autogenous bone, metal wedges, or a custom implant. Biomechanically the custom implant is superior to the other choices but its intraoperative use is difficult to always predict, even with CAD-CAM designs. Incorporation of bone graft in peripheral defects has a success rate of 90 per cent and its use is recommended when the peripheral defect involves 50 per cent or more of the bony support of either tibial plateau and the defect is greater than 5 mm in depth.

Patellar resurfacing is recommended in the presence of inflammatory arthritis and is controversial in osteoarthritis. Patellofemoral problems are the most frequent source of complications in total knee arthroplasty. Their occurrence ranges from 1.5 to 10 per cent and they include instability, fracture of the patella, wear, patella ligament rupture, and soft tissue impingement. Maintenance of quadriceps function and avoidance of infection are key factors in the management of these problems (Figs. 17, 18) 2484,2485.

Failure of total knee replacement when indicated, is treated with revision surgery. Careful preoperative evaluation of soft tissue, presence of infection, stability, and bone loss are important in the planning of revision total knee arthroplasty (Fig. 19) 2486. Complications are similar to primary arthroplasty with a higher infection rate (2 - 5 per cent). The satisfactory results for revision total knee arthroplasty, with limited follow-up, are approximately 70 per cent.

Infection after total knee arthroplasty is between 1 and 2 per cent. Rand and Fitzgerald have reported an incidence of 2.2 per cent in a 14-year total knee arthroplasty study. Perioperative antibiotics and clean air operating rooms have made the incidence of this complication low. Increased infection rates are associated with revision surgery, the use of a hinge prosthesis, immunocompromised patients, and patients with chronic skin ulcerations on their lower extremities. Treatment of infections in the immediate postoperative period is with early aggressive surgical debridement and antibiotics; treatment is successful in 80 per cent of patients. Chronic infections are treated most effectively by two-stage reimplantation. An antibiotic impregnated cement spacer has gained popularity as an adjunct to the management of the infection. Retraction of soft tissues is prevented to some degree with the use of the spacer and enough stability is achieved to allow ambulation. Successful treatment of prosthetic infections is more likely in Gram-positive infections. Reimplantation should be considered on an individual basis after initial aggressive debridement and an adequate course of appropriate antibiotics.

Surgical alternatives to reimplantation are arthrodesis, resection arthroplasty, and rarely amputation. Suppressive antibiotics alone are used in patients who are not surgical candidates. The major disadvantage to resection arthroplasty is a high incidence of significant pain and functional limitation. In view of this, treatment by pseudoarthrosis is limited to patients with limited ambulatory status. Arthrodesis can provide a stable and painless extremity, although fusion rates are variable. Removal of a constrained prosthesis with associated bone loss has a 56 per cent rate of fusion. Less constrained prostheses have a higher fusion rate of approximately 80 per cent.

Peroneal nerve palsy is a rare complication following total knee arthroplasty. Severe valgus and flexion deformities have a greater likelihood of having this complication. Prophylactic decompression of the peroneal nerve does not prevent its occurrence postoperatively.

Supracondylar fracture of the femur following total knee arthroplasty has an incidence approaching 2.5 per cent. This complication is associated with osteoporosis and notching of the femur. Improved instrumentation, an increased inventory of sizes of prosthesis, and alertness of the surgeon should decrease notching of the femur.

Thromboembolic complications are the bane of surgery on the lower extremity. The incidence of deep vein thrombosis in total knee arthroplasty is high, and in patients with no perioperative prophylaxis, the incidence is 84 per cent. The incidence despite prophylaxis with either heparin, warfarin, or aspirin was 57 per cent in the same study. Fatal pulmonary emboli after total knee arthroplasty is less frequent than after surgery but its incidence is unknown.

All patients should be considered for perioperative prophylaxis against deep vein thrombosis.

Improving longevity of total knee arthroplasty and the limited life of an arthrodesis has made arthrodesis of the knee as a primary procedure uncommon. The most common indication for arthrodesis of the knee is septic failure of a total knee replacement (Fig. 20) 2487. Additional indications for arthrodesis include post-traumatic arthritis in the young, painful ankylosis, neuromuscular disease, and the neuropathic joint. Arthrodesis in the neuropathic joint has a high failure rate, and in selected cases, total knee arthroplasty has been successful. Neuromuscular disorders typically include poliomyelitis with absent quadriceps function. Stabilization of the knee with a hinged knee brace may be effective but if significant recurvatum is present, arthrodesis may be an effective consideration for surgical management.

Complications of arthrodesis of the knee include non-union, recurrent sepsis, fracture, and patient dissatisfaction. Non-union following attempts at arthrodesis of the knee may be as high as 50 per cent if significant bone loss is present. The development of a fibrous ankylosis may not always be painful, but if pain is present, a secondary procedure will be required. Persistent infection can result even with achieving fusion, after septic failure of total knee arthroplasty. Dissatisfaction with knee arthrodesis is high and conversion to total knee replacement is not recommended.

Disorders of the patellofemoral joint are manifested by either pain, instability, or a combination of both. Patellofemoral arthralgia may be the result of chondromalacia patellae, abnormalities of patella alignment, or pathology of the retinaculum.

Abnormalities of the cartilage are graded according to their severity. Grade I is softening of the cartilage, Grade II is fibrillation of less than 1.3 cm, Grade III fibrillation is greater than 1.3 cm, Grade IV is exposed bone. Pathological change of the patellofemoral joint is a result of repeated loading of the cartilage beyond its ability to withstand deformation. This is usually the result of abnormal joint mechanics involving the patellofemoral articulation. Pain can be extremely disabling with associated functional limitations. Instability patterns of the patellofemoral joint result in lateral subluxation or dislocation of the patella. Chronic instability may occur as a result of an acute traumatic dislocation, rotational malalignment to the lower extremity, ligamentous laxity, excessive quadriceps angle, patella alta, neuromuscular disorders, and either patella or femoral anatomic variation.

Evaluation of the patient with patellofemoral pain and instability should include in the physical examination, concentration of the location of pain, the rotational and axial alignment of the extremity, patellar mobility, and pronation of the foot. Radiographic evaluation should include either a Lauren or Merchant axial view and supplementary CT or MRI scanning with midpatella views at 0⁰, 10⁰, 20⁰, and 30⁰ are helpful in diagnosing subtleties of malalignment.

Treatment initially is usually non-operative emphasizing rehabilitation, strengthening of the quadriceps, and stretching of the hamstrings, iliotibial band, and retinaculum. Elastic knee supports, orthotics, and anti-inflammatory medication are additionally helpful for the symptomatic patient. Operative treatment consists of realignment procedures for malalignment disorders.

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