Knee joint replacement

Knee joint replacement

There are three compartments within the knee: medial and lateral tibiofemoral, and patellofemoral. In 20–50% of cases, OA a ff ects only one compartment and these patients may be suitable for a partial or unicompartmental knee replacement (UKR) ( Figure 40.4 ), while in tricompartmental disease a TKR is indicated ( Figure 40.5 ). Patients are suitable for UKR if disease is limited to one com partment, if ligaments are intact and if fixed deformity is less than 15°. UKR has complication rates of one-third to one-half those of TKR with a lower infection rate, lower medical risks and lower risk of death. UKR is associated with a more rapid recovery , shorter hospital stay , preservation of knee kinemat - ics and generally superior function to that of TKR. Revision rates for UKR are significantly influenced by the surgeon’s experience and the implant. In optimal conditions the revision rates are similar to TKR, but on national registries UKRs have higher 10-y ear revision rates (6–12 %) than TKRs (2–6%). Isolated patellofemoral replacement is also performed but the numbers are low in view of the scarcity of isolated patellofemoral disease. Revision rates are higher than other partial knee replacements, largely because of progression of arthritis in the remaining compartments. A TKR can be regarded as a resurfacing procedure in which the femoral articular surface is replaced with metal and the tibial articular surface is replaced by a tough polyethylene insert, usually inserted into a metal tibial baseplate. TKR is one of the most successful sur gical interventions, with most patients getting significant pain reduction and improvement in mobility . Revision rates are less than 5% at 15 years. Patient satisfaction with TKR is generally lower than that achieved with hip replacement. TKR implants are generally cemented into the bone using polymethylmethacrylate (PMMA) cement. The design of the articulation can provide varying amounts of stability or con - straint. Unconstrained TKRs are the most common and can either retain or sacrifice the PCL; these implants are called cruciate-retaining (CR) or PCL-sacrificing (PS), respectively . The more constrained the implant the greater the force trans - mitted to the implant–cement–bone interfaces, therefore increasing the risk of loosening. More constrained implants are generally only used in revision cases. If the joint is very unstable or deformed then a hinged knee replacement is used as it does not rely on the lig aments for stability . Modern knee replacements try to reduce wear by using enhanced bearing surfaces such as cross-linked polyethylene, vitamin E-enriched polyethylene or ceramicised surface coatings. The TKR surgical technique aims to correct the deformity and leave the leg aligned with the mechanical axis and with the joint parallel to the ground. More modern philosophies of TKR try to match the patient’s more individual alignment in the hope that this feels more natural to the patient, but it - may require additional technology to allow this to be done accurately , e.g. computer navigation or robotics. It is important

Figure 40.5 Anteroposterior (a) and lateral (b) radiographs of a total knee replacement.

balanced to allow good stability , range of motion and patellar tracking. Early weight-bearing and mobilising are now possi ble, with some patients treated as day cases but most staying in hospital for 2–4 days. Complications following TKR can be broadly classified into intraoperative and postoperative ( Table 40.2 ). /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF Summary box 40.4 Aims of TKR /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF

TABLE 40.2 Complications of total knee replacement. Intraoperative Implant malposition and malalignment; with subsequent contribution to instability, stiffness or pain Nerve or vessel injury, including tourniquet damage Fracture Patellar tendon avulsion Fat embolism Postoperative Infection Deep vein thrombosis/pulmonary embolism Pain/stiffness Instability Osteolysis Component loosening Dislocation Correct deformity caused by arthritis Align the knee to the mechanical axis or slightly under- corrected Joint line perpendicular to the mechanical axis Balanced collateral ligaments Ensure patellofemoral joint tracks normally

Knee joint replacement

There are three compartments within the knee: medial and lateral tibiofemoral, and patellofemoral. In 20–50% of cases, OA a ff ects only one compartment and these patients may be suitable for a partial or unicompartmental knee replacement (UKR) ( Figure 40.4 ), while in tricompartmental disease a TKR is indicated ( Figure 40.5 ). Patients are suitable for UKR if disease is limited to one com partment, if ligaments are intact and if fixed deformity is less than 15°. UKR has complication rates of one-third to one-half those of TKR with a lower infection rate, lower medical risks and lower risk of death. UKR is associated with a more rapid recovery , shorter hospital stay , preservation of knee kinemat - ics and generally superior function to that of TKR. Revision rates for UKR are significantly influenced by the surgeon’s experience and the implant. In optimal conditions the revision rates are similar to TKR, but on national registries UKRs have higher 10-y ear revision rates (6–12 %) than TKRs (2–6%). Isolated patellofemoral replacement is also performed but the numbers are low in view of the scarcity of isolated patellofemoral disease. Revision rates are higher than other partial knee replacements, largely because of progression of arthritis in the remaining compartments. A TKR can be regarded as a resurfacing procedure in which the femoral articular surface is replaced with metal and the tibial articular surface is replaced by a tough polyethylene insert, usually inserted into a metal tibial baseplate. TKR is one of the most successful sur gical interventions, with most patients getting significant pain reduction and improvement in mobility . Revision rates are less than 5% at 15 years. Patient satisfaction with TKR is generally lower than that achieved with hip replacement. TKR implants are generally cemented into the bone using polymethylmethacrylate (PMMA) cement. The design of the articulation can provide varying amounts of stability or con - straint. Unconstrained TKRs are the most common and can either retain or sacrifice the PCL; these implants are called cruciate-retaining (CR) or PCL-sacrificing (PS), respectively . The more constrained the implant the greater the force trans - mitted to the implant–cement–bone interfaces, therefore increasing the risk of loosening. More constrained implants are generally only used in revision cases. If the joint is very unstable or deformed then a hinged knee replacement is used as it does not rely on the lig aments for stability . Modern knee replacements try to reduce wear by using enhanced bearing surfaces such as cross-linked polyethylene, vitamin E-enriched polyethylene or ceramicised surface coatings. The TKR surgical technique aims to correct the deformity and leave the leg aligned with the mechanical axis and with the joint parallel to the ground. More modern philosophies of TKR try to match the patient’s more individual alignment in the hope that this feels more natural to the patient, but it - may require additional technology to allow this to be done accurately , e.g. computer navigation or robotics. It is important

Figure 40.5 Anteroposterior (a) and lateral (b) radiographs of a total knee replacement.

balanced to allow good stability , range of motion and patellar tracking. Early weight-bearing and mobilising are now possi ble, with some patients treated as day cases but most staying in hospital for 2–4 days. Complications following TKR can be broadly classified into intraoperative and postoperative ( Table 40.2 ). /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF Summary box 40.4 Aims of TKR /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF

TABLE 40.2 Complications of total knee replacement. Intraoperative Implant malposition and malalignment; with subsequent contribution to instability, stiffness or pain Nerve or vessel injury, including tourniquet damage Fracture Patellar tendon avulsion Fat embolism Postoperative Infection Deep vein thrombosis/pulmonary embolism Pain/stiffness Instability Osteolysis Component loosening Dislocation Correct deformity caused by arthritis Align the knee to the mechanical axis or slightly under- corrected Joint line perpendicular to the mechanical axis Balanced collateral ligaments Ensure patellofemoral joint tracks normally

Knee joint replacement

There are three compartments within the knee: medial and lateral tibiofemoral, and patellofemoral. In 20–50% of cases, OA a ff ects only one compartment and these patients may be suitable for a partial or unicompartmental knee replacement (UKR) ( Figure 40.4 ), while in tricompartmental disease a TKR is indicated ( Figure 40.5 ). Patients are suitable for UKR if disease is limited to one com partment, if ligaments are intact and if fixed deformity is less than 15°. UKR has complication rates of one-third to one-half those of TKR with a lower infection rate, lower medical risks and lower risk of death. UKR is associated with a more rapid recovery , shorter hospital stay , preservation of knee kinemat - ics and generally superior function to that of TKR. Revision rates for UKR are significantly influenced by the surgeon’s experience and the implant. In optimal conditions the revision rates are similar to TKR, but on national registries UKRs have higher 10-y ear revision rates (6–12 %) than TKRs (2–6%). Isolated patellofemoral replacement is also performed but the numbers are low in view of the scarcity of isolated patellofemoral disease. Revision rates are higher than other partial knee replacements, largely because of progression of arthritis in the remaining compartments. A TKR can be regarded as a resurfacing procedure in which the femoral articular surface is replaced with metal and the tibial articular surface is replaced by a tough polyethylene insert, usually inserted into a metal tibial baseplate. TKR is one of the most successful sur gical interventions, with most patients getting significant pain reduction and improvement in mobility . Revision rates are less than 5% at 15 years. Patient satisfaction with TKR is generally lower than that achieved with hip replacement. TKR implants are generally cemented into the bone using polymethylmethacrylate (PMMA) cement. The design of the articulation can provide varying amounts of stability or con - straint. Unconstrained TKRs are the most common and can either retain or sacrifice the PCL; these implants are called cruciate-retaining (CR) or PCL-sacrificing (PS), respectively . The more constrained the implant the greater the force trans - mitted to the implant–cement–bone interfaces, therefore increasing the risk of loosening. More constrained implants are generally only used in revision cases. If the joint is very unstable or deformed then a hinged knee replacement is used as it does not rely on the lig aments for stability . Modern knee replacements try to reduce wear by using enhanced bearing surfaces such as cross-linked polyethylene, vitamin E-enriched polyethylene or ceramicised surface coatings. The TKR surgical technique aims to correct the deformity and leave the leg aligned with the mechanical axis and with the joint parallel to the ground. More modern philosophies of TKR try to match the patient’s more individual alignment in the hope that this feels more natural to the patient, but it - may require additional technology to allow this to be done accurately , e.g. computer navigation or robotics. It is important

Figure 40.5 Anteroposterior (a) and lateral (b) radiographs of a total knee replacement.

balanced to allow good stability , range of motion and patellar tracking. Early weight-bearing and mobilising are now possi ble, with some patients treated as day cases but most staying in hospital for 2–4 days. Complications following TKR can be broadly classified into intraoperative and postoperative ( Table 40.2 ). /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF Summary box 40.4 Aims of TKR /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF

TABLE 40.2 Complications of total knee replacement. Intraoperative Implant malposition and malalignment; with subsequent contribution to instability, stiffness or pain Nerve or vessel injury, including tourniquet damage Fracture Patellar tendon avulsion Fat embolism Postoperative Infection Deep vein thrombosis/pulmonary embolism Pain/stiffness Instability Osteolysis Component loosening Dislocation Correct deformity caused by arthritis Align the knee to the mechanical axis or slightly under- corrected Joint line perpendicular to the mechanical axis Balanced collateral ligaments Ensure patellofemoral joint tracks normally