Instability currently represents the most frequent cause for revision total knee replacement. Instability can be primary from the standpoint of inadequately performed collateral and/or posterior cruciate ligament balancing during primary total knee replacement or it may be secondary to malalignment secondary to loosening and settling of the implants which can develop later progressive instability. Revision surgery must take into consideration any component malalignment that may have primarily contributed to instability. Also, collateral ligament integrity may change following total knee replacement slightly after complete correction of a severe deformity that presents rarely as instability after several months.

Care should be given to assessing collateral ligament integrity. This can be done during physical examination by manual or radiological stress testing to see if the mediolateral stress of the knee comes to a good endpoint. If there is no sense of a palpable endpoint, then the surgeon must assume structural incompetency of the medial or lateral collateral ligament or both. In posterior cruciate ligament retaining knees, anteroposterior instability must be assessed.

For instability, most revisions will require a posterior cruciate substituting design or a constrained unlinked condylar design. Occasionally, a posterior cruciate ligament preserving design can be used in situations where the bone-stock is well preserved and the posterior cruciate ligament shows excellent structural integrity. However, if the patient displays considerable global instability, a linked, rotating platform constrained total knee replacement design will be required. Recent data has shown that the rotating hinges work quite well in restoring stability to the knee with maintenance of the clinical results over a considerable length of time. Revision can range from simple polyethylene insert exchange to a thicker dimension, isolated component revision or complete revision of both femoral and tibial devices.

During revision surgery, laminar spreaders may be utilised to assess the flexion and extension spaces after the tibial platform is restored. If a symmetric flexion and extension space is achieved, then the collateral ligaments are intact. Depending on the remaining existing bone stock, a posterior stabilised or constrained condylar unlinked prosthesis may be used for implantation. In cases with considerable asymmetry or a large flexion/extension mismatch, a rotating hinge design should be utilised.

Intramedullary stems should be utilised in most cases when bone integrity is suspect and insufficient. Currently, stems should be placed cementless to permit easier future revision. Cementing the stems is only recommended if there is lack of intramedullary isthmic support or there is a hip prosthetic stem that prohibits a stem from engaging the isthmic cortex. However, it should be realised that later revision of the fully cemented revision implant may be quite difficult.

Infection should be ruled out by aspiration off of antibiotics prior to any revision operation, especially if loosening of the components represents the cause of instability early. The surgeon should attempt to restore collateral ligament balance whenever possible as this yields the best clinical result.

Introduction

Several studies have shown that functional outcomes are similar regardless of being discharged directly to home or to a rehabilitation center after total knee arthroplasty (TKA). Therefore, we sought to determine if there is a difference in patient care or patient satisfaction for patients discharged to in-patient rehabilitation or home-based rehabilitation.

Instability currently represents the most frequent cause for revision total knee replacement. Instability can be primary from the standpoint of inadequately performed collateral and/or posterior cruciate ligament balancing during primary total knee replacement or it may be secondary to malalignment secondary to loosening which can develop later progressive instability. Revision surgery must take into consideration any component malalignment that may have primarily contributed to instability.

Care should be given to assessing collateral ligament integrity. This can be done during physical examination by manual or radiological stress testing to see if the mediolateral stress of the knee comes to a good endpoint. If there is no sense of a palpable endpoint, then the surgeon must assume structural incompetency of the medial or lateral collateral ligament or both. In posterior cruciate ligament retaining knees, anteroposterior instability must be assessed.

For instability, most revisions will require a posterior cruciate substituting design or a constrained unlinked condylar design that, although sometimes a posterior cruciate ligament preserving design can be used in situations where the bone-stock is well preserved. However, if the patient displays considerable global instability, a linked, rotating platform constrained total knee replacement design will be required. Recent data has shown that the rotating hinges work quite well in restoring stability to the knee with maintenance of the clinical results over a considerable length of time.

During revision surgery, laminar spreaders may be utilised to assess the flexion and extension spaces after the tibial platform is restored. If a symmetric flexion and extension space is achieved, then the collateral ligaments are intact. Depending on the remaining existing bone stock, a posterior stabilised or constrained condylar unlinked prosthesis may be used for implantation. In cases with considerable asymmetry or a large flexion/extension mismatch, then a rotating hinge design should be utilised.

Intramedullary stems should be utilised in most cases when bone integrity is suspect and insufficient. Currently, stems should be placed cementless to permit easier future revision. Cementing the stems is only recommended if there is lack of intramedullary isthmic support or there is a hip prosthetic stem that prohibits a stem from engaging the isthmic cortex. However, it should be realised that later revision of the fully cemented revision implant may be quite difficult.

Infection should be ruled out by aspiration off of antibiotics prior to any revision operation, especially if loosening of the components represents the cause of instability. The surgeon should attempt to restore collateral ligament balance whenever possible as this yields the best clinical result.

Rotating Hinge total knee replacement designs are currently more frequently used for revision total knee replacement. As the designs of these implants have improved over time, the threshold for using them has been lowered. Cases of global instability and severe bone loss have not been adequately addressed by the standard use of unlinked constrained designs. Recurrent dislocation and polyethylene post failure due to cold flow and wear make the use of the unlinked designs insufficient to address the mechanical forces developed in a grossly unstable knee.

The linked rotating hinge designs have been able to address global ligamentous instability in four planes. Medial-lateral instability is well addressed by these implants. In cases of severe ankylosis with large flexion contractures, it is often necessary to resect the distal femur above the femoral insertions of the medial and lateral collateral ligaments. The absence of the tethering effect of severely contracted collateral ligaments demand the need for linked designs, although there has been reported success with the use of unlinked designs. Rotating hinges are particularly important for use in cases of recurvatum where an extension stop is incorporated in the design. The design permits slight hyperextension which permits application to clinical situations with incompetent quadriceps strength or paralysis.

The clinical results are quite acceptable even though most reports present 65–75% success rates. However, it should also be stated that these patient cohorts represent the most severe cases of revision surgery. Current hinged designs should continue to lower the threshold for use.

An important goal of total knee replacement is deformity correction. Arthritic narrowing can be accompanied by a fixed shortening of the collateral ligament on the same side of the narrowing. There can also be ligamentous laxity that develops in the opposite compartment. Flexion contracture can develop with tightening of the posterior capsule. Successful total knee replacement requires proper bone resection along with gap balancing and balanced collateral ligament tensioning. Beware of correctable deformities, as the collateral ligament may have kept its resting length and therefore the knee becomes stable after the bone resections are made and the spacer block is inserted to test the stability of the knee in flexion and extension.

In the varus knee, the MCL may be contracted. A medial release of the superficial medial collateral ligament may be necessary. This can be done by stripping the periosteal insertion of the MCL. A stretch may be accomplished by placing a laminar spreader in the narrow medial joint space and opening the space until the MCL stretches from its insertion. This maneuver will require a further increase in polyethylene thickness height of 2 – 4mm. Krackow has also on occasion done a surgical imbrication of the LCL, if it appears attenuated on the lateral side of a severe varus deformity.

For valgus deformities, the LCL, arcuate ligament and popliteus and ITB can be contracted. At this time, most authors recommend preservation of the popliteus tendon as it affects primarily the flexion gap. In extension there has been consensus that the surgeon should release what is tight. This may include the ITB release in a pie-crust fashion, or off the Gerdy's tubercle and then a selective release of the arcuate ligament complex. Krackow has also utilised tightening imbrication of the MCL if it is severely attenuated and lax. This has been used infrequently, however. To avoid overlengthening of the knee by referencing balance off of the lengthened, attenuated MCL in cases of severe valgus deformity, less release is performed and a CCK implant may be used.

For severe flexion contractures, the posterior osteophytes should be first aggressively removed. The posterior joint capsule can be stripped off the distal femur and sometimes the gastrocnemius muscle insertions can be dissected free. After these maneuvers, proximal raising of the joint line by resection of the distal femur can be utilised. In ankylosis with severe flexion contracture, constrained implants will be needed if the proximal resection extends above the insertion of the collateral ligaments.

Recurvatum is a rarely seen deformity that is usually associated with an extraordinarily weak or paretic quadriceps. The joint capsule has become stretched over time. Careful balancing of the knee is necessary. But, if the recurvatum still persists, distally augmenting the femur is an option. And no releases are required.

A key component to the success of total knee replacement is the health and integrity of the extensor mechanism. While there are issues related to the patella, such as fracture, dislocation, subluxation, clunk due to peripatellar fibrosis and anterior knee pain, the overall integrity of the extensor mechanism is of tantamount importance in providing an excellent functional outcome. During total knee replacement it is of utmost importance to preserve the anatomic insertion of the patellar tendon on the tibial tubercle. However, after total knee replacement, a fall or extreme osteoporosis of the patella may cause a rupture of the patellar tendon, distally or proximally, and possibly the quadriceps tendon off of the proximal pole of the patella.

Simple repairs of the patellar tendon avulsion may involve use of the semitendonosis and gracilis tendons along with primary repair of the tendon. Usually, patella infera develops after such a repair affecting overall strength and function. For severe disruptions of the extensor mechanism that are accompanied by a significant extensor lag, autologous tissue repair may not be possible. Thus, there are three techniques for reconstruction of this difficult problem: Extensor mechanism allograft with bone-patellar tendon-patella-quadriceps tendon, extensor mechanism allograft with os calcis-Achilles tendon construct and Marlex-mesh reconstruction for patellar tendon avulsion.

The key to success of extensor mechanism allograft is proper tensioning of the allograft at full extensor and immobilisation for 6 weeks. Rosenberg's early experience showed that the allograft works best placed at maximum tension in extension. Rubash has described the use of the os calcis-Achilles tendon which does not utilise a patellar substitute. Hansen has recently described excellent results with the use of Marlex mesh to act as a structural reinforcement to the patellar tendon when it is avulsed.

Exposure in revision total knee replacement can be quite challenging due to scar formation from one or many previous incisions. Disruption of the patellar or quadriceps tendon during revision must be avoided at all costs and many surgical maneuvers have been described to permit safe exposure in order to remove the implants during the initial stage of reconstruction. Standard maneuvers include recreation of the medial and lateral gutters, patient dissection to allow the soft tissue to stretch over time and proximal medial exposure of the tibia and release of the semimembranosis tendon insertion.

There are three specialised techniques for exposure during revision total knee replacement: the quadriceps snip as described by Insall, the V-Y quadriceps turndown as described by Coonse and Adams, and the tibial tubercle osteotomy as described by Whiteside.

The quadriceps snip is a proximal lateral extension of the medial arthrotomy used during a standard approach. It is easy to perform and can be used for most revision situations. This is should be the standard first choice for gaining exposure in revision surgery. The V-Y quadriceps turndown is quite extensile and is a combination of a lateral retinacular release connected to the proximal portion of the medial arthrotomy. Although it allows excellent exposure in revision situations, it is associated with extensor weakness and extensor lag. The Whiteside tibial tubercle osteotomy is also a versatile approach. Care should be taken to preserve a lateral periosteal sleeve, and subsequent repair with wire presents the best healing possibility. It is quite elegant in providing access to the proximal tibia to facilitate removal of a well fixed, stemmed tibial component.

A key component to the success of total knee replacement is the health and integrity of the extensor mechanism. While there are issues related to the patella, such as fracture, dislocation, subluxation, clunk due to peripatellar fibrosis and anterior knee pain, the overall integrity of the extensor mechanism is of tantamount importance in providing an excellent functional outcome. During total knee replacement it is of utmost importance to preserve the anatomic insertion of the patellar tendon on the tibial tubercle. However, after total knee replacement, a fall or extreme osteoporosis of the patella may cause a rupture of the patellar tendon, distally or proximally, and possibly the quadriceps tendon off of the proximal pole of the patella.

Simple repairs of the patellar tendon avulsion may involve use of the semitendonosis and gracilis tendons along with primary repair of the tendon. Usually, patella infera develops after such a repair affecting overall strength and function. For severe disruptions of the extensor mechanism that are accompanied by a significant extensor lag, autologous tissue repair may not be possible. Thus, there are three techniques for reconstruction of this difficult problem: Extensor mechanism allograft with bone-patellar tendon-patella-quadriceps tendon, extensor mechanism allograft with os calcis-Achilles tendon construct and Marlex-mesh reconstruction for patellar tendon avulsion.

The key to success of extensor mechanism allograft is proper tensioning of the allograft at full extensor and immobilisation for 6 weeks. Rosenberg's early experience showed that the allograft works best placed at maximum tension in extension. Rubash has described the use of the os calsis-Achilles tendon which does not utilise a patellar substitute. Hansen has recently described excellent results with the use of Marlex mesh to act as a structural reinforcement to the patellar tendon when it is avulsed.

Exposure in revision total knee replacement can be quite challenging due to scar formation from one or many previous incisions. Disruption of the patellar or quadriceps tendon during revision must be avoided at all costs and many surgical maneuvers have been described to permit safe exposure in order to remove the implants during the initial stage of reconstruction. Standard manoeuvres include recreation of the medial and lateral gutters, patient dissection to allow the soft tissue to stretch over time and proximal medial exposure of the tibia and release of the semimembranosis tendon insertion.

There are three specialised techniques for exposure during revision total knee replacement: the quadriceps snip as described by Insall, the V-Y quadriceps turndown as described by Coonse and Adams, and the tibial tubercle osteotomy as described by Whiteside.

The quadriceps snip is a proximal lateral extension of the medial arthrotomy used during a standard approach. It is easy to perform and can be used for most revision situations. This is should be the standard first choice for gaining exposure in revision surgery. The V-Y quadriceps turndown is quite extensile and is a combination of a lateral retinacular release connected to the proximal portion of the medial arthrotomy. Although it allows excellent exposure in revision situations, it is associated with extensor weakness and extensor lag. The Whiteside tibial tubercle osteotomy is also a versatile approach. Care should be taken to preserve a lateral periosteal sleeve, and subsequent repair with wire presents the best healing possibility. It is quite elegant in providing access to the proximal tibia to facilitate removal of a well fixed, stemmed tibial component.

Osteosarcoma is the most common malignant bone tumour in children and young people. Approximately 40% patients respond poorly to highly toxic preoperative MAP (methotrexate adriamycin, cisplatin) chemotherapy with consequent inferior survival. The role of genetic polymorphisms in drug response and toxicity is reported in acute leukaemia and some solid tumours. Recent evidence in osteosarcoma suggests increased chemotherapy toxicity is associated with improved survival. The aim of this pilot study is to investigate the influence of drug target and metabolising gene polymorphisms on tumour response and chemotherapy toxicity in osteosarcoma.

Patients who have completed MAP chemotherapy are eligible. Chemotherapy toxicity (CTCAE grade) is collected from patient records. Tumour response is graded as good (> 90% necrosis) or poor (< 90% necrosis) in resection specimen. Peripheral blood DNA is typed for genome-wide single nucleotide polymorphisms (SNP) using the Illumina 610 Quad array and analysed using Bead Studio software. Standard PCR techniques are used to genotype the Thymidylate synthase (TS) gene (folate pathway) for the presence of 2 or 3 copies of a 28 base pair repeat (2R/3R) and a G/C SNP in the 3R allele.

52 patients have entered to date: 33 good responders, 12 poor and 7 unevaluable for response. Median age 18 years (range 10–51), males:females 1.3:1. Median follow up is 39 months (range 2–76) with 11 patients relapsing. 23 patients have TS genotype 2R/2R, nineteen 2R/3R, six 3R/3R, three 2R/4R and one 2R/7R. Neither TS repeat or G/C SNP genotype correlated with histological response or degree of methotrexate stomatitis. Interestingly, presence of the 2R allele was significantly related to relapse (p=0.01) but may reflect small patient numbers. Recurrent methotrexate stomatitis (> 2 episodes of CTCAE grade 2) was weakly correlated with no relapse (p=0.07). Analysis of SNP array data with emphasis on MAP pathway polymorphisms will be presented when complete.