FRCS: Knee

Resect more distal femur. It is important to ensure balanced flexion and extension during total knee replacement. As a general rule, if the knee is tight in flexion and extension, the tibia is addressed. If the knee is tight in either flexion or extension, the femur is addressed. There are different methods which may be used including: Tight in flexion and extension – (i) decrease polyethylene insert size; (ii) resect more proximal tibia Tight in extension only – (i) resect additional distal femur; (ii) posterior capsular release Tight in flexion only – (i) downsize the femoral component; (ii) recess and release the posterior cruciate ligament; (iii) resect a posterior slope on the tibia; (iv) release the posterior capsule

Fatigue wear. Fatigue wear (also referred to as delamination or catastrophic wear) is the usual cause of failure of the polyethylene in total knee replacements. Subsurface failure occurs due to repeated loading, and the surface layer of the polyethylene breaks off. Adhesive wear is due to a junction forming between two surfaces as they come into contact. Two-body abrasive wear relates to wear between two surfaces of different hardness and third-body abrasive wear occurs when extra material appears between two opposing surfaces. Corrosive wear occurs between metals and not polyethylene.

Its primary role is proprioceptive. Although the ACL has a major role in proprioception, receiving innervation from the tibial nerve, its primary role is as a restraint to anterior tibial displacement. The average length is 38 mm, and it has a small anteromedial and a bulky posterolateral bundle. It arises from a femoral attachment at the posteromedial corner of the medial aspect of the lateral femoral condyle in the intercondylar notch and inserts into a tibial attachment in a fossa in front of and lateral to the anterior tibial spine.

The superficial medial collateral ligament is part of layer 1 of the medial structures of the knee. The layers of the knee are as follows: 107 Lateral Layer 1 – iliotibial tract, biceps (common peroneal nerve lies between layer 1 and 2) Layer 2 – patellar retinaculum, patellofemoral ligament Layer 3 superficial – lateral collateral ligament (LCL), fabellofibular ligament (lateral geniculate artery runs between deep and superficial layer) Layer 3 deep – arcuate ligament, coronary ligament, popliteus tendon, popliteofibular ligament, capsule Medial Layer 1 – sartorius and fascia (gracilis, semitendinosis, and saphenous nerve run between layer 1 and 2) Layer 2 – semimembranosus, superficial medial collateral ligament (MCL), posterior oblique ligament Layer 3 – deep MCL, capsule There are two meniscofemoral ligaments which arise from the posterior horn of the lateral meniscus and insert into the substance of the posterior cruciate ligament; the ligament of Humphrey lies anterior to the ligament of Wrisberg. The posterior cruciate ligament is approximately 38 mm in length and arises from the antero-lateral aspect of the medial femoral condyle in the area of intercondylar notch and inserts into the tibial sulcus, over the back of tibial plateau approximately 1 cm distal to the joint line. It is composed of an anterolateral and posteromedial bundle and is supplied by the middle genicular artery.

Internal rotation of the tibial component. Patellar maltracking can occur following incorrect component positioning. Internal rotation and medial placement of the femoral component, and lateral placement of the patellar component lead to more lateral alignment of the patella within the trochlear groove. Internal rotation and medial placement of the tibial component lead to a lateralized tibial tubercle, and hence increased Q-angle.

Autologous chondrocyte implantation. Non-steroidal anti-inflammatory drugs, partial or total knee replacement, and high tibial osteotomy (opening or closing) are acceptable treatment for isolated medial compartment osteoarthritis. Other modalities would include physiotherapy, alternative analgesics, supplements, braces and intra-articular injections. Autologous chondrocyte implantation, whilst shown to be effective for treating isolated chondral defects, is not effective for treating osteoarthritis.

Open washout/debridement, polyethylene exchange and intravenous antibiotics. This patient presents with an early prosthetic infection. The accepted treatment is an open debridement and intravenous antibiotics. Arthroscopic washout can be effective in some situations, but intravenous antibiotics alone are not likely to be successful. Single or staged revision is acceptable treatment for an infected joint replacement, but would not be used in the first instance, and is reserved for if the initial treatment fails. 108

There is a poorer implant survivorship in patients with rheumatoid arthritis. Raising or lowering the joint line during total knee replacement can have an adverse effect on range of motion, patellar function and stability, and can lead to early revision. The accepted safe distance for altering the joint line is 8 mm. The minimum thickness of an ultra-high-molecular-weight polyethylene insert is 6–8 mm; thinner implants are associated with earlier failure due to fatigue wear. Contraindications to total knee replacement include a deficient extensor mechanism, infection, vascular deficiency and neuromuscular abnormalities affecting the muscles around the knee. Patients with rheumatoid arthritis have a lower risk of failure of total knee replacement; other good prognostic variables are age over 60 and use of a condylar prosthesis with a metal-backed tibial component. Following patellectomy, it is thought there are increasing stresses on the posterior cruciate ligament, resulting in deficiency and greater anteroposterior instability if the ligament is not substituted.

Deficient anterior cruciate ligament. A high tibial, valgus-producing osteotomy, either lateral closing or medial opening, is an effective surgical option for medial compartment osteoarthritis. It suits younger patients with varus alignment, fixed flexion less than 15º and flexion greater than 90º. Contraindications include lateral compartment degeneration, loss of a significant portion of the lateral meniscus, lateral tibial subluxation of greater than 1 cm, medial compartment bone loss, symptomatic patellofemoral degeneration, inflammatory arthritis and poor patient compliance. Anterior cruciate ligament deficiency alone is not a contraindication.

Microscopy and culture of joint aspirate. The diagnosis of periprosthetic infection soon after surgery is difficult. Both erythrocyte sedimentation rate and C-reactive protein are likely to be elevated due to the post-operative inflammation and a triple phase bone scan would not be able to distinguish between infection and early post-surgical changes. The definitive test in this situation is analysis of a joint aspiration. Radiographs and magnetic resonance imaging are unlikely to be of diagnostic benefit.

Patella baja. Patellofemoral disorders are extremely common and tend to have a mutlifactorial aetiology. Predisposing factors include the condition femoral anteversion, lateral patella tilt, patella alta (not baja), a reduced trochlea sulcus and a lateral tibial tuberosity. Others include gluteal dysfunction, vastus medialis oblique dysfunction, tight iliotibial band, tight rectus femoris, tight calves/hamstrings, lateral tibial torsion and increased foot pronation.

During hamstring harvesting, the connection between the semitendinosus and the medial gastrocnemius must be divided. There continues to be debate as to the exact positioning of graft tunnels during ACL reconstruction, but it is generally accepted that the femoral tunnel should be placed posteriorly on the lateral wall of the notch. Therefore, for right knees this is the 10 or 11 o’clock position and for left knees the 1 or 2 o’clock position, and the tunnel should be on 109 the posterior half of Blumensaat’s line. There is also debate as to the optimal fixation method, but there is no evidence to support interference being better than suspensory. A number of connections (vinculae) exist with the hamstrings and these must be divided to avoid insufficient harvesting. A fairly predictable vincula exists between semitendinosus and medial gastrocnemius, although anatomical studies have shown that a number of vinculae can be present between both semitendinosus and gracilis and the popliteal fascia, sartorius, gastrocnemius, pretibial and superficial fascia.

Their primary role is to provide anteroposterior stability to the knee. The medial meniscus is semicircular in length and about 3 cm long; the lateral meniscus is more circular in shape. The medial meniscus is more fixed than the lateral, which explains the greater incidence of medial meniscal tears compared to lateral. Discoid menisci are more common in the lateral side; the reported incidence is 4–15.5% for lateral versus 0.06–0.3% for medial. The menisci are made up of an extracellular matrix, composed of water and mainly type 1 collagen, as well as glycoproteins, elastin and proteoglycans. The menisci have a number of roles; the principal function is that of load transmission; additional functions are increasing joint conformity, synovial fluid distribution and providing anteroposterior stability.

Division of the infrapatellar branch of the saphenous nerve. The anterior cutaneous branches of the femoral nerve consist of the intermediate cutaneous nerve and medial cutaneous nerve. These nerves communicate with the terminal branches of the lateral femoral cutaneous nerve and the infrapatellar branch of the saphenous nerve to form the patellar plexus. The patient’s numbness may have been caused by all of the mechanisms described, but with the midline incision for total knee replacement, it is injury to the infrapatellar branch of the saphenous nerve which is the most likely cause.

Arthroscopic or open debridement. This patient is describing patellar clunk syndrome. This occurs when a fibrous nodule of tissue forms in the undersurface of the quadriceps tendon just above the patella. It is a problem with posterior stabilized knee replacements but can also occur in cruciate retaining designs. As the knee extends the nodule impinges in box of femoral component and with continued extension it jumps out with an audible or palpable clunk. Non-operative treatment is usually not successful and debridement of the nodule is requited.

Patients over 80 years should not have a unicompartmental knee replacement. The contraindications to unicompartmental knee replacement include anterior cruciate deficiency, inflammatory arthropathy, fixed varus deformity and medial or lateral subluxation. Patellofemoral arthritis is not always considered an absolute contraindication. Although often carried out in younger patients, if the indications are correct, a unicompartmental knee replacement can be carried out at any age. There is continued debate about unicompartmental versus total knee replacement and it is the subject of on-going trials. However, there is evidence to support better subjective results in unicompartmental; this may be due to a better ‘feel’, owing to the fact that both cruciate ligaments are retained. Simultaneous anterior cruciate ligament reconstruction and unicompartmental knee has been described. 110

They do not have a better survivorship. A number of theoretical benefits exist with mobile-bearing knee replacements compared to fixed bearing. Although many have demonstrated good results, there is no good evidence to suggest superiority over fixed-bearing implants. This applies to wear, range of motion, objective and subjective outcome scores and implant survival. Although often used in younger patients, there is no contraindication to their use in older patients.

Patella baja. Total knee replacement after a proximal tibial osteotomy presents a number of technical difficulties. Studies have shown that these knee replacements are more prone to complications such as persisting pain, malalignment and infections. Any number of problems can be encountered during surgery, but the most common is patella baja, seen with both opening and closing wedge osteotomies, although more commonly in the latter. Another important consideration is the change in tibial slope as closing wedge tends to decrease the posterior tibial slope and opening wedge increases it.

Degenerative meniscal tears are a relative contraindication to repair. Meniscal repairs are increasingly carried out, perhaps due to the introduction of all-inside techniques with various devices. They have not, however, been shown to be more effective than the open techniques. Consistently better results are achieved in younger patients, with relatively fresh peripheral tears, in stable (or stabilized) knees. Tears through degenerate menisci are unlikely to heal. For an inside-out lateral meniscal repair, the capsule is exposed between the iliotibial band and biceps tendon, followed by posterior retraction of the gastrocnemius. Saphenous nerve injury is more common with an inside-out technique compared to an all-inside technique for medical meniscus repair.

A posteromedial approach between medial gastrocnemius and semimembranosus. The tibial insertion of the posterior cruciate ligament is best exposed through a posteromedial approach between medial gastrocnemius and semimembranosus. The former is retracted laterally and inferiorly, pulling the nerves and vessels out of the way to reach the posteromedial corner of the joint. The posterolateral corner of the joint is exposed between the lateral head of the gastrocnemius and biceps femoris muscle. Muscle-splitting approaches are generally not used at the back of the knee.

An injury with external tibial rotation with the knee at 90
of flexion is likely to injure the posterior cruciate and lateral collateral ligaments. Neuromuscular training indeed explains the gender difference in the incidence of anterior cruciate ligament in similar sports, but it is higher in women. Furthermore, women have a greater total valgus knee loading when landing from a jump. A grade 3 posterior cruciate ligament injury does not necessarily need reconstruction. The majority of grade 1 and 2 injuries can be treated with protected weight bearing and quadriceps rehabilitation. Grade 3 injuries require immobilization in full extension for 2 to 4 weeks to protect the posterior cruciate ligament and the other posterolateral structures presumed to be damaged. Prophylactic knee bracing has not been shown to reduce anterior cruciate ligament injuries in contact sports, but has been shown to reduce medial collateral ligament injuries. 111

The condition is more common on the lateral than medial femoral condyle. Osteochondritis dissecans is a lesion of subchondral bone that results in subchondral delamination and sequestration with or without articular mantle involvement. It is more common in males (5:3), bilateral in 20%, and more common on the medial femoral condyle (4:1). Healing potential is greater in younger patients and open growth plates are considered a good prognostic factor. Pappas classification describes the age at detection: I – below 12 years, II – 12 to 20 years and III – above 20 years. The Guhl classification is based on arthroscopic appearance: I – intact lesion, II – early separation (stable flap), III – partial detachment and IV – complete detachment.

Fibrocartilage. Microfracture involves making multiple holes through the subchondral plate at the base of the articular cartilage defect. This allows undifferentiated mesenchymal stem cells to proliferate in the defect, and they subsequently differentiate into fibrocartilage. There is initially a high proportion of type II collagen but this reverts to predominantly type I collagen. The resulting ‘cartilage’ fill is not as hard wearing as true hyaline cartilage, but the procedure has been shown to produce long-lasting symptomatic relief.

The middle genicular artery. The middle genicular artery supplies the anterior and posterior cruciate ligaments and the synovial membrane. The medial superior genicular supplies the vastus medialis, lower femur and the knee joint. The lateral superior genicular supplies the vastus lateralis, lower femur and the knee joint. The medial inferior genicular supplies the upper end of the tibia and the articulation of the knee.

Tunnel placement is less important when using synthetic grafts. A femoral tunnel in the roof of the notch (12 o’clock position) would result in a vertical graft. This would restore anteroposterior stability, but would not impact on the rotational stability. Several reference points are described for the tibial tunnel. These include the anterior border of the posterior cruciate ligament (10–11 mm anterior to) and the posterior border of the anterior horn of the lateral meniscus (along a line from this point to the tibial spine). Mal-positioning of the femoral tunnel can limit post-operative range of motion; an anterior tunnel could limit flexion and a posterior tunnel could limit extension. Tunnel placement is probably even more important when using synthetic grafts as these are less forgiving of mal-positioning.

Revision to a constrained knee prosthesis. Medial collateral ligament deficiency in a total knee replacement may present with pain, instability or both. A knee brace may provide a temporary solution. Repair or reconstruction of the ligament is unlikely to provide the necessary valgus resistance, and the only sensible option is to revise to a constrained prosthesis. There is some debate as to whether this can be a high posted design (non-linked) or whether it has to be hinged. 112 1. Which of the following nerves supply the greatest area of sensibility of the foot? a. Sural. b. Saphenous. c. Tibial. d. Deep peroneal. e. Superficial peroneal. 2. A 32-year-old man sustains a Lisfranc fracture dislocation. Which of the following is the most important factor in predicting a satisfactory outcome? a. Severity of initial injury. b. The state of the articular cartilage. c. The age of the patient. d. The smoking status of the patient. e. Whether or not a compensation claim is involved. 3. Which of the following is not typically associated with a ball and socket ankle joint? a. Absent fibula. b. Deficient knee ligaments. c. An equinovarus deformity. d. Talocalcaneal coalition. e. Proximal femoral focal deficiency. 4. A vertical talus is most commonly associated with which of the following? a. Oligohydramnios. b. Arthrogryposis. c. Congenital talipes equinovarus. d. Tarsal coalition. e. Developmental dysplasia of the hip. 5. A 13-year-old girl who enjoys ballet presents with a painful big toe whilst performing. The likely diagnosis is? a. Hallux valgus. b. Hallux rigidus. # Cambridge University Press 2012. 119