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Minimally Invasive Quadriceps-Sparing Posterior Stabilized Total Knee Arthroplasty
Minimally Invasive Quadriceps-Sparing Posterior Stabilized Total Knee Arthroplasty Michael S. Shin, MD,* Rodney K. Alan, MD,† and Alfred J. Tria, Jr, MD*,† Quadriceps-sparing total knee arthroplasty is a minimally invasive surgery for total knee replacement. The first procedures were performed by the senior author and by Thomas M. Coon, MD, in February 2002. The instruments and the surgical technique have gradually improved, and there is now a minimally invasive tibial implant (MIS Tibia, Zimmer Orthopaedics, Warsaw, IN) that facilitates insertion of the prosthesis. This article will outline the procedure as performed for a posterior stabilized total knee design (Legacy High Flex Knee, Zimmer Orthopaedics). The results show less blood loss, less pain, a shorter hospital stay, faster recovery of range of motion, and faster return to normal activity. Oper Tech Orthop 16:170-176 © 2006 Elsevier Inc. All rights reserved. KEYWORDS total knee arthroplasty, MIS total knee, posterior stabilized total knee arthroplasty, knee, knee replacement
S
ince the introduction of the total condylar knee replacement in 1974, continuous improvements and ongoing modifications have changed the face of total knee arthroplasty (TKA).1-3 The result of these modifications has led to excellent long-term outcomes.4 Other adjustments have been made to facilitate component implantation and surgical technique. Some of these alterations have truly been advancements and have withstood the test of time and the rigors of objective testing, whereas others, including arthroscopic-assisted procedures, have fallen out of favor. With the success of minimally invasive unicondylar knee arthroplasty (UKA) in reducing morbidity, blood loss, hospital stay, and recovery time5-8 the latest innovation in joint arthroplasty has been to extend the techniques and principles of minimally invasive surgery to TKAs. These changes have been made with the overall goal of improving outcomes for the patient. Ideally, minimally invasive surgery for TKA should maintain or improve on the longevity of standard TKA, maintain the quality and safety of traditional TKAs, and decrease the morbidity and recovery time. “Mini” TKA has contributed a decreased surgical incision length and decreased soft tissue disruption. The minimized
*Department of Orthopaedic Surgery, Robert Wood Johnson Medical School, Piscataway, NJ. †Institute for Advanced Orthopaedic Study, Orthopaedic Center of New Jersey, Somerset, NJ. Address reprint requests to Alfred J. Tria, Jr, MD, Institute for Advanced Orthopaedic Study, Orthopaedic Center of New Jersey, 1527 State Highway 27, Suite 1300, Somerset, NJ 08873. E-mail: [email protected]
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approaches typically incise the quadriceps tendon, the vastus medialis, or the subvastus interval.9-15 The quadriceps-sparing (QS) TKA uses a capsular incision that extends from the superior pole of the patella to 2 cm below the tibial joint line. The benefit of the QS minimally invasive technique is aligned with the mini-principles but aims to maintain the complete integrity of the extensor mechanism. The surgical approach of QS TKA does not extend the arthrotomy proximally into the quadriceps tendon, the vastus medialis, or the subvastus interval. The short-term results are promising and have shown to benefit patients with earlier increased range of motion (ROM), shorter hospital stay, decreased blood loss, decreased pain, and earlier return to function without compromising alignment, knee scores, and patient safety.16,17
Indications The indications for the surgery are much more restrictive than the standard TKA. The patient should have symptomatic, radiographically confirmed osteoarthritis that has failed medical management. Patella baja is a relative contraindication because it is more difficult to sublux the patella laterally. Patients with rheumatoid arhritis are not the best candidates because the bone is often osteoporotic and can be injured during the course of the surgery with the smaller approach. The patient should be in good overall medical health and should not have significant comorbidities that would preclude an operation that may be 50% longer than a standard TKA. The knee alignment should be no greater than 10° of varus, 15° of valgus, or 10° of flexion contracture. Obesity
Minimally invasive quadriceps-sparing posterior stabilized TKA
Figure 1 The leg holder allows both flexion-extension and internalexternal rotation.
also represents a problem for the surgery and an overall weight of 225 pounds is used as a cutoff. Body mass index has not proven to be helpful at all. The distribution of the weight and the relationship between the thigh length and knee circumference is more important and it may be possible to establish a ratio of these 2 measurements that will be most useful. The knee should have at least 105° of motion. The anatomy of the vastus medialis has some effect on the degree of difficulty of the exposure. There are 3 types of insertions for the vastus medialis: a high insertion into the quadriceps tendon above the level of the patella, a standard insertion into the superomedial aspect of the patella, and a low insertion at the midportion of the patella. The lower the insertion, the more difficult the exposure becomes. The vastus insertion into the midlevel of the patella makes the procedure extremely difficult and is an indication for extension of the exposure and for the use a Mini approach. During the past 3 years, the senior author has seen a gradual increase in the number of QS surgeries that have been performed. The percentage has increased from 28% to 50% of the entire number of arthroplasties per year. This increase is more related to the referral patterns of the practice than to any change in the indications.
171 in line with the skin incision from the superomedial border of the patella approximately 2 cm below the tibial joint line. Both the varus and valgus knee can be replaced through the medial arthrotomy; however, a lateral arthrotomy similar to one for a lateral UKA can be used for the valgus knee. With either approach, care is taken to avoid extension of the arthrotomy into the quadriceps tendon, the vastus medialis, or the subvastus interval. The knee is then brought into full extension and the patellar fat pad is excised. Without fully everting the patella, the articular surface is removed using a free hand technique with an oscillating saw. A patellar clamp is currently under development to eliminate the need for free hand resurfacing. The patellar cut is performed early in the procedure to provide more working room in the knee joint. Resurfacing of the patella is not mandatory but facilitates the exposure. A metal protector is placed over the patellar surface to shield it from the retractors that are used throughout the remainder of the procedure (Fig. 3). Although the knee remains in full extension, the anterior surface of the femur is cleared to visualize the femoral sulcus for later femoral sizing and positioning. The QS MIS TKA can accommodate both posterior stabilized and cruciate retaining prosthetic designs. The senior author prefers the posterior stabilized design, and this chapter is directed to that technique. The knee is then flexed to 45° and the anterior and posterior cruciate ligaments are resected from the intercondylar notch. After resection of the cruciates and visualization of the notch, the anteroposterior axis line of Whiteside is established (Fig. 4) and an intramedullary rod is introduced into the femoral canal (Fig. 5). A cutting guide is then attached to the intramedullary reference and the distal femur is resected from medial to lateral. During the distal femoral cutting, the intramedullary reference must be removed and the cut must be completed by using the partially cut condyles to guide the saw blade for the remainder of the resection. The tibial surface is resected next using an extramedullary guide. The alignment guide for the quadriceps sparing sys-
Surgical Technique The patient is positioned supine on the operating room table and a tourniquet is applied to the upper thigh. The leg is sterilely prepped and draped in the traditional fashion and a leg holder (Innovative Medical Products, Plainville, CT) is used for positioning of the limb throughout the entire procedure (Fig. 1). The leg holder is valuable in this type of surgery because the knee is typically in the flexed position from 30 ° to 60° for most of the operation and holding this by hand is cumbersome and time consuming. Most of the surgeries are performed under tourniquet control. A curvilinear skin incision is made from the superior pole of the patella to the tibial joint line just medial to the patella and patella tendon (Fig. 2). This is essentially the same incision used for the minimally invasive medial compartment UKA. An arthrotomy is made
Figure 2 The medial incision extends from the superior margin of the patella to 2 cm below the joint line. (A) Tibiofemoral joint line; (B) medial femoral condyle margin.
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tem is very similar to that for a standard total knee but it directs the saw blade from the medial aspect of the tibia (Fig. 6). The varus-valgus, flexion-extension, and depth of the resection are all controlled in a similar fashion to a standard cutting guide. After alignment of the tibial guide is completed, the cut is initiated with the knee in 70° of flexion. Sometimes, the tibial surface can be resected as a single piece, similar to the standard technique. However, if the soft tissues are particularly stiff, or the knee is a larger size, it may be necessary to cut the tibial proximal fragment into two or three pieces to facilitate the removal and to protect the posterior neurovascular structures. The three piece approach removes the medial one half of the tibia as a single piece similar to the resection for a medial UKA. The lateral one half is then cut into two pieces, anterior and posterior and removed in sequence (Fig. 7). With both the distal femoral and proximal tibial resections completed, the extension space is checked with a spacer block and extramedullary rods (Fig. 8). Ligament balancing is conducted in the normal fashion with the standard soft
Figure 4 Whiteside’s anteroposterior axis line is drawn on the surface of the femur. (Color version of figure is available online.)
Figure 3 The metal protector is placed on the patellar cut surface to protect it from the retractors during the remainder of the procedure. (A) The metal patellar protector has 4 legs for impaction into the bone. (B) The patellar protector in position. (Color version of figure is available online.)
tissue releases. With the 20 mm of bone resected from the surfaces, it is not difficult to release either the medial collateral ligament complex or the iliotibial band and the lateral ligament complex. Once alignment and balance in extension are confirmed, the knee is flexed to 70° and the femoral sizing guide (tower) is used to set the external rotation and to determine the size of the femoral component (Fig. 9). The tower references the posterior condyles of the femur but must also be adjusted so that it is parallel to the anteroposterior axis line if either condyle is deficient posteriorly. A probe is attached to the tower and used to reference the anterior femur for sizing (Fig. 10). A preliminary cut is made across the anterior surface of the femur, setting the rotation and avoiding cortical notching. The finishing block is positioned medial to lateral in full extension (Fig. 11), and the cuts are completed with the knee in 70° of flexion (Fig. 12). After completion of the femoral and tibial cuts, the working space in the knee is dramatically increased. The final checks of the flexion and extension gaps are completed and alignment and balance are adjusted in the standard fashion. The tibial sizing plate is attached to a curved handle that avoids internal rotation. The guide has two deployable hooks that reference the posterior cortex of the proximal tibia (Fig. 13). The plate is centered medial to lateral and externally rotated using the tibial tubercle, the femoral box cut, and the malleoli of the ankle as reference points. The drilling and broaching are completed in the standard fashion.
Minimally invasive quadriceps-sparing posterior stabilized TKA
173 will often lead to difficulties with exposure and lead to early failures. During the QS surgery, the tibia is seldom completely subluxed anterior to the femur. Therefore, the cuts must be made with the knee in different degrees of flexion and extension as opposed to the standard open knee arthroplasty that references the knee either in full extension or at 90° of flexion. The distal femoral cut and the proximal tibial cut are performed with a captured saw blade from medial to lateral. This orientation is different than the standard approach and, with less visibility of the posterior aspect of the knee, the surgeon must be sure to protect the neurovascular structures. The femoral cut does become much easier with experience. The tibial cut can deviate from the perpendicular because the lateral aspect is not fully visualized. This problem can be overcome with proper soft-tissue retraction and is almost eliminated with the new electromagnetic navigation monitoring that the senior author is now using. Cement removal is a bit more tedious with the MIS tech-
Figure 5 (A) The intramedullary guide is inserted into the femoral canal with a plate that references the medial femoral condyle. (B) The side cutting guide is attached to the intramedullary plate on the medial side of the femur. (Color version of figure is available online.)
The trial components are inserted in the following order: tibia, femur, polyethylene tray, and patella. Patellar tracking, ligament balance, range of motion, and overall alignment are checked for the final time before cementing. The bone surfaces are prepared and the components are cemented in the same order as the trial components. The tibial component is now two pieces with a stem that is inserted through the plate and torqued into position. The shorter keel on the implant makes it much easier to insert in full extension and allows improved visualization for the cementing (Fig. 14). The tourniquet is released before closure and drains are placed for cell saver suction. Physical therapy is started on the afternoon of surgery with full weight bearing as tolerated. DVT prophylaxis is begun on the first day after surgery with enoxaparin. The patients remain in the hospital for two days and are, then, transferred to a rehabilitation center.
Pitfalls The most important way to avoid many of the pitfalls is to choose the appropriate knee for the surgical procedure. Expanding the indications is sometimes enticing; however, it
Figure 6 (A) The extramedullary tibial cutting guide directs the saw blade from the medial aspect of the knee. (B) The medial one half of the proximal tibial resection can be removed using a technique similar to the unicondylar resection. Then, the saw blade can be inserted into the slot cut to complete the lateral resection. (Color version of figure is available online.)
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Figure 9 The tower is an instrument that references the posterior femoral condyles and sets the external rotation of the femoral cuts. (Color version of figure is available online.) Figure 7 (A) The proximal tibial resected bone can be removed using a 3-piece technique if the knee is tight or the fragment is of a larger size. This figure shows the anteroposterior cut with a reciprocating saw in an open knee procedure. (B) The white arrows shows the previous anteroposterior cut and the black arrow traces the oblique cut from medial to lateral to remove the anterolateral fragment. (Color version of figure is available online.)
nique. Palacos cement is much easier to use because of its prolonged doughy phase and the components should be cemented with separate mixes. The tibial component is cemented first. The MIS tibia is much easier to position in full extension and the lateral side of the knee is much easier to see with the new prosthesis. It is important to fully visualize the
Figure 8 The extension space is checked using a standard spacer block and extramedullary rods. (Color version of figure is available online.)
Figure 10 The anterior reference arm measures the size of the femoral component and sets the location of the preliminary external rotation cut. (Color version of figure is available online.)
Minimally invasive quadriceps-sparing posterior stabilized TKA
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Figure 11 A plate is attached to the femoral finishing block and rests on the anterior cut surface. The block is centered medial to lateral and pinned in place. (Color version of figure is available online.)
lateral aspect of the tibia during the cementing. The tibia should be kept under compression with a spacer block while waiting to cement the femoral component. There have been three tibial loosenings and these seem to have occurred because of liftoff of the tray while the cement is setting up. Male knees with extremely large femoral components are difficult to complete and the surgeon should not hesitate it extend the incision if necessary.
Results The senior author has now completed more than 400 of the MIS QS surgeries since February of 2002. The procedure now requires approximately 50% more time than the standard TKA. The blood loss is 20% less, as measured by intraoperative and postoperative cell-saver collections and transfusions. The average length of stay has decreased by 2 days from the standard TKA. Pain scores, pain medicine require-
Figure 13 (A) The tibial sizing plate has 2 posterior hooks that can be deployed to reference the posterior cortex of the tibia on either the medial or lateral side, or both. (B) The handle for the tibial plate angles around the patellar tendon to avoid internally rotating the component while positioning the plate. (Color version of figure is available online.)
Figure 12 The knee is flexed to 70° and the finishing cuts are completed. (Color version of figure is available online.)
ments, and physical therapy participation have all improved in the quadriceps sparing TKA population when compared with the standard TKA. Greater ROM in the range of 20 to 30° has been measured for quadriceps sparing TKA, and this difference persists for at least 3 months. Postoperative alignment as determined radiographically has shown no statistically significant difference overall from matched controls un-
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ments, and time till participation in physical therapy while concurrently increasing early ROM.16,17 The findings have also shown Knee Society Scores and radiographic alignment outcomes that are comparable to standard TKAs without significantly increasing complications or compromising patient safety. The short-term results appear to be promising. Longterm results and clinical trials comparing the different MIS techniques will certainly need to be completed; however, there is little doubt that smaller exposures and limited arthrotomies will become more common in the next few years.
References
Figure 14 (A) The MIS tibial component has a shorter keel for ease of insertion. (B) A drop-down screw can be inserted through the tray. (Color version of figure is available online.)
dergoing standard TKA over the same time period and Knee Society Scores are the same in both populations. There are 3 tibial component loosenings, 1 early infection, 2 late infections, and 2 tibial components are in 7° of varus. Two of the tibial loosenings have been revised using a standard tibial tray with a stem. The early infected knee was removed and reimplanted with success. The 2 varus tibias have not required surgical correction. One of the late infections has been removed and reinserted and the other is pending further surgery.
Conclusions Minimally invasive TKAs are in the early stages of development and are improving in a step-wise fashion. The QS MIS TKA does not violate the extensor mechanism or the suprapatellar pouch. The early results have shown decreased blood loss, hospital stay, pain scores, pain medication require-
1. Insall J, Ranawat CS, Scott WN, et al: Total condylar knee replacement: preliminary report. Clin Orthop Relat Res 120:149-154, 1976 2. Insall J, Tria AJ, Scott WN: The total condylar knee prosthesis: the first 5 years. Clin Orthop Relat Res 145:68-77, 1979 3. Insall JN, Hood RW, Flawn LB, et al: The total condylar knee prosthesis in gonarthrosis. A five to nine-year follow-up of the first one hundred consecutive replacements. J Bone Joint Surg 65:619-28, 1983 4. NIH Consensus Statement on Total Knee Replacement December 8-10. J Bone Joint Surg Am 86A:1328-1335, 2004 5. Repicci JA, Eberle RW: Minimally invasive surgical technique for unicondylar knee arthroplasty. J South Orthop Assoc Spring; 8:20-27, 1999 6. Argenson JN, Flecher X: Minimally invasive unicompartmental knee arthroplasty. Knee 11:341-347, 2004 7. Price AJ, Webb J, Topf H, et al: Oxford Hip and Knee Group: Rapid recovery after oxford unicompartmental arthroplasty through a short incision. J Arthroplasty 16:970-976, 2001 8. Gesell MW, Tria AJ Jr: MIS unicondylar knee arthroplasty: surgical approach and early results. Clin Orthop Relat Res 428:53-60, 2004 9. Scuderi GR, Tenholder M, Capeci C: Surgical approaches in miniincision total knee arthroplasty. Clin Orthop Relat Res 428:61-67, 2004 10. Bonutti PM, Mont MA, McMahon M, et al: Minimally invasive total knee arthroplasty. J Bone Joint Surg Am 86A:26-32, 2004 (suppl) 11. Haas SB, Cook S, Beksac B: Minimally invasive total knee replacement through a mini midvastus approach: a comparative study. Clin Orthop Relat Res 428:68-73, 2004 12. Laskin RS: Minimally invasive total knee replacement using a mini-mid vastus incision technique and results. Surg Technol Int 13:231-238, 2004 13. Laskin RS, Beksac B, Phongjunakorn A, et al: Minimally invasive total knee replacement through a mini-midvastus incision: an outcome study. Clin Orthop Relat Res 428:74-81, 2004 14. Laskin RS: Minimally invasive total knee arthroplasty: the results justify its use. Clin Orthop Relat Res 440:54-59, 2005 15. Boerger TO, Aglietti P, Mondanelli N, et al: Mini-subvastus versus medial parapatellar approach in total knee arthroplasty. Clin Orthop Relat Res 440:82-87, 2005 16. Tria AJ, Coon TM: Minimal incision total knee arthroplasty: early experience. Clin Orthop Relat Res 416:185-190, 2003 17. Berger RA, Sanders S, Gerlinger T, et al: Outpatient total knee arthroplasty with a minimally invasive technique. J Arthroplasty 20:33-38, 2005 (suppl)
S
ince the introduction of the total condylar knee replacement in 1974, continuous improvements and ongoing modifications have changed the face of total knee arthroplasty (TKA).1-3 The result of these modifications has led to excellent long-term outcomes.4 Other adjustments have been made to facilitate component implantation and surgical technique. Some of these alterations have truly been advancements and have withstood the test of time and the rigors of objective testing, whereas others, including arthroscopic-assisted procedures, have fallen out of favor. With the success of minimally invasive unicondylar knee arthroplasty (UKA) in reducing morbidity, blood loss, hospital stay, and recovery time5-8 the latest innovation in joint arthroplasty has been to extend the techniques and principles of minimally invasive surgery to TKAs. These changes have been made with the overall goal of improving outcomes for the patient. Ideally, minimally invasive surgery for TKA should maintain or improve on the longevity of standard TKA, maintain the quality and safety of traditional TKAs, and decrease the morbidity and recovery time. “Mini” TKA has contributed a decreased surgical incision length and decreased soft tissue disruption. The minimized
*Department of Orthopaedic Surgery, Robert Wood Johnson Medical School, Piscataway, NJ. †Institute for Advanced Orthopaedic Study, Orthopaedic Center of New Jersey, Somerset, NJ. Address reprint requests to Alfred J. Tria, Jr, MD, Institute for Advanced Orthopaedic Study, Orthopaedic Center of New Jersey, 1527 State Highway 27, Suite 1300, Somerset, NJ 08873. E-mail: [email protected]
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1048-6666/06/$-see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1053/j.oto.2006.05.004
approaches typically incise the quadriceps tendon, the vastus medialis, or the subvastus interval.9-15 The quadriceps-sparing (QS) TKA uses a capsular incision that extends from the superior pole of the patella to 2 cm below the tibial joint line. The benefit of the QS minimally invasive technique is aligned with the mini-principles but aims to maintain the complete integrity of the extensor mechanism. The surgical approach of QS TKA does not extend the arthrotomy proximally into the quadriceps tendon, the vastus medialis, or the subvastus interval. The short-term results are promising and have shown to benefit patients with earlier increased range of motion (ROM), shorter hospital stay, decreased blood loss, decreased pain, and earlier return to function without compromising alignment, knee scores, and patient safety.16,17
Indications The indications for the surgery are much more restrictive than the standard TKA. The patient should have symptomatic, radiographically confirmed osteoarthritis that has failed medical management. Patella baja is a relative contraindication because it is more difficult to sublux the patella laterally. Patients with rheumatoid arhritis are not the best candidates because the bone is often osteoporotic and can be injured during the course of the surgery with the smaller approach. The patient should be in good overall medical health and should not have significant comorbidities that would preclude an operation that may be 50% longer than a standard TKA. The knee alignment should be no greater than 10° of varus, 15° of valgus, or 10° of flexion contracture. Obesity
Minimally invasive quadriceps-sparing posterior stabilized TKA
Figure 1 The leg holder allows both flexion-extension and internalexternal rotation.
also represents a problem for the surgery and an overall weight of 225 pounds is used as a cutoff. Body mass index has not proven to be helpful at all. The distribution of the weight and the relationship between the thigh length and knee circumference is more important and it may be possible to establish a ratio of these 2 measurements that will be most useful. The knee should have at least 105° of motion. The anatomy of the vastus medialis has some effect on the degree of difficulty of the exposure. There are 3 types of insertions for the vastus medialis: a high insertion into the quadriceps tendon above the level of the patella, a standard insertion into the superomedial aspect of the patella, and a low insertion at the midportion of the patella. The lower the insertion, the more difficult the exposure becomes. The vastus insertion into the midlevel of the patella makes the procedure extremely difficult and is an indication for extension of the exposure and for the use a Mini approach. During the past 3 years, the senior author has seen a gradual increase in the number of QS surgeries that have been performed. The percentage has increased from 28% to 50% of the entire number of arthroplasties per year. This increase is more related to the referral patterns of the practice than to any change in the indications.
171 in line with the skin incision from the superomedial border of the patella approximately 2 cm below the tibial joint line. Both the varus and valgus knee can be replaced through the medial arthrotomy; however, a lateral arthrotomy similar to one for a lateral UKA can be used for the valgus knee. With either approach, care is taken to avoid extension of the arthrotomy into the quadriceps tendon, the vastus medialis, or the subvastus interval. The knee is then brought into full extension and the patellar fat pad is excised. Without fully everting the patella, the articular surface is removed using a free hand technique with an oscillating saw. A patellar clamp is currently under development to eliminate the need for free hand resurfacing. The patellar cut is performed early in the procedure to provide more working room in the knee joint. Resurfacing of the patella is not mandatory but facilitates the exposure. A metal protector is placed over the patellar surface to shield it from the retractors that are used throughout the remainder of the procedure (Fig. 3). Although the knee remains in full extension, the anterior surface of the femur is cleared to visualize the femoral sulcus for later femoral sizing and positioning. The QS MIS TKA can accommodate both posterior stabilized and cruciate retaining prosthetic designs. The senior author prefers the posterior stabilized design, and this chapter is directed to that technique. The knee is then flexed to 45° and the anterior and posterior cruciate ligaments are resected from the intercondylar notch. After resection of the cruciates and visualization of the notch, the anteroposterior axis line of Whiteside is established (Fig. 4) and an intramedullary rod is introduced into the femoral canal (Fig. 5). A cutting guide is then attached to the intramedullary reference and the distal femur is resected from medial to lateral. During the distal femoral cutting, the intramedullary reference must be removed and the cut must be completed by using the partially cut condyles to guide the saw blade for the remainder of the resection. The tibial surface is resected next using an extramedullary guide. The alignment guide for the quadriceps sparing sys-
Surgical Technique The patient is positioned supine on the operating room table and a tourniquet is applied to the upper thigh. The leg is sterilely prepped and draped in the traditional fashion and a leg holder (Innovative Medical Products, Plainville, CT) is used for positioning of the limb throughout the entire procedure (Fig. 1). The leg holder is valuable in this type of surgery because the knee is typically in the flexed position from 30 ° to 60° for most of the operation and holding this by hand is cumbersome and time consuming. Most of the surgeries are performed under tourniquet control. A curvilinear skin incision is made from the superior pole of the patella to the tibial joint line just medial to the patella and patella tendon (Fig. 2). This is essentially the same incision used for the minimally invasive medial compartment UKA. An arthrotomy is made
Figure 2 The medial incision extends from the superior margin of the patella to 2 cm below the joint line. (A) Tibiofemoral joint line; (B) medial femoral condyle margin.
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tem is very similar to that for a standard total knee but it directs the saw blade from the medial aspect of the tibia (Fig. 6). The varus-valgus, flexion-extension, and depth of the resection are all controlled in a similar fashion to a standard cutting guide. After alignment of the tibial guide is completed, the cut is initiated with the knee in 70° of flexion. Sometimes, the tibial surface can be resected as a single piece, similar to the standard technique. However, if the soft tissues are particularly stiff, or the knee is a larger size, it may be necessary to cut the tibial proximal fragment into two or three pieces to facilitate the removal and to protect the posterior neurovascular structures. The three piece approach removes the medial one half of the tibia as a single piece similar to the resection for a medial UKA. The lateral one half is then cut into two pieces, anterior and posterior and removed in sequence (Fig. 7). With both the distal femoral and proximal tibial resections completed, the extension space is checked with a spacer block and extramedullary rods (Fig. 8). Ligament balancing is conducted in the normal fashion with the standard soft
Figure 4 Whiteside’s anteroposterior axis line is drawn on the surface of the femur. (Color version of figure is available online.)
Figure 3 The metal protector is placed on the patellar cut surface to protect it from the retractors during the remainder of the procedure. (A) The metal patellar protector has 4 legs for impaction into the bone. (B) The patellar protector in position. (Color version of figure is available online.)
tissue releases. With the 20 mm of bone resected from the surfaces, it is not difficult to release either the medial collateral ligament complex or the iliotibial band and the lateral ligament complex. Once alignment and balance in extension are confirmed, the knee is flexed to 70° and the femoral sizing guide (tower) is used to set the external rotation and to determine the size of the femoral component (Fig. 9). The tower references the posterior condyles of the femur but must also be adjusted so that it is parallel to the anteroposterior axis line if either condyle is deficient posteriorly. A probe is attached to the tower and used to reference the anterior femur for sizing (Fig. 10). A preliminary cut is made across the anterior surface of the femur, setting the rotation and avoiding cortical notching. The finishing block is positioned medial to lateral in full extension (Fig. 11), and the cuts are completed with the knee in 70° of flexion (Fig. 12). After completion of the femoral and tibial cuts, the working space in the knee is dramatically increased. The final checks of the flexion and extension gaps are completed and alignment and balance are adjusted in the standard fashion. The tibial sizing plate is attached to a curved handle that avoids internal rotation. The guide has two deployable hooks that reference the posterior cortex of the proximal tibia (Fig. 13). The plate is centered medial to lateral and externally rotated using the tibial tubercle, the femoral box cut, and the malleoli of the ankle as reference points. The drilling and broaching are completed in the standard fashion.
Minimally invasive quadriceps-sparing posterior stabilized TKA
173 will often lead to difficulties with exposure and lead to early failures. During the QS surgery, the tibia is seldom completely subluxed anterior to the femur. Therefore, the cuts must be made with the knee in different degrees of flexion and extension as opposed to the standard open knee arthroplasty that references the knee either in full extension or at 90° of flexion. The distal femoral cut and the proximal tibial cut are performed with a captured saw blade from medial to lateral. This orientation is different than the standard approach and, with less visibility of the posterior aspect of the knee, the surgeon must be sure to protect the neurovascular structures. The femoral cut does become much easier with experience. The tibial cut can deviate from the perpendicular because the lateral aspect is not fully visualized. This problem can be overcome with proper soft-tissue retraction and is almost eliminated with the new electromagnetic navigation monitoring that the senior author is now using. Cement removal is a bit more tedious with the MIS tech-
Figure 5 (A) The intramedullary guide is inserted into the femoral canal with a plate that references the medial femoral condyle. (B) The side cutting guide is attached to the intramedullary plate on the medial side of the femur. (Color version of figure is available online.)
The trial components are inserted in the following order: tibia, femur, polyethylene tray, and patella. Patellar tracking, ligament balance, range of motion, and overall alignment are checked for the final time before cementing. The bone surfaces are prepared and the components are cemented in the same order as the trial components. The tibial component is now two pieces with a stem that is inserted through the plate and torqued into position. The shorter keel on the implant makes it much easier to insert in full extension and allows improved visualization for the cementing (Fig. 14). The tourniquet is released before closure and drains are placed for cell saver suction. Physical therapy is started on the afternoon of surgery with full weight bearing as tolerated. DVT prophylaxis is begun on the first day after surgery with enoxaparin. The patients remain in the hospital for two days and are, then, transferred to a rehabilitation center.
Pitfalls The most important way to avoid many of the pitfalls is to choose the appropriate knee for the surgical procedure. Expanding the indications is sometimes enticing; however, it
Figure 6 (A) The extramedullary tibial cutting guide directs the saw blade from the medial aspect of the knee. (B) The medial one half of the proximal tibial resection can be removed using a technique similar to the unicondylar resection. Then, the saw blade can be inserted into the slot cut to complete the lateral resection. (Color version of figure is available online.)
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Figure 9 The tower is an instrument that references the posterior femoral condyles and sets the external rotation of the femoral cuts. (Color version of figure is available online.) Figure 7 (A) The proximal tibial resected bone can be removed using a 3-piece technique if the knee is tight or the fragment is of a larger size. This figure shows the anteroposterior cut with a reciprocating saw in an open knee procedure. (B) The white arrows shows the previous anteroposterior cut and the black arrow traces the oblique cut from medial to lateral to remove the anterolateral fragment. (Color version of figure is available online.)
nique. Palacos cement is much easier to use because of its prolonged doughy phase and the components should be cemented with separate mixes. The tibial component is cemented first. The MIS tibia is much easier to position in full extension and the lateral side of the knee is much easier to see with the new prosthesis. It is important to fully visualize the
Figure 8 The extension space is checked using a standard spacer block and extramedullary rods. (Color version of figure is available online.)
Figure 10 The anterior reference arm measures the size of the femoral component and sets the location of the preliminary external rotation cut. (Color version of figure is available online.)
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Figure 11 A plate is attached to the femoral finishing block and rests on the anterior cut surface. The block is centered medial to lateral and pinned in place. (Color version of figure is available online.)
lateral aspect of the tibia during the cementing. The tibia should be kept under compression with a spacer block while waiting to cement the femoral component. There have been three tibial loosenings and these seem to have occurred because of liftoff of the tray while the cement is setting up. Male knees with extremely large femoral components are difficult to complete and the surgeon should not hesitate it extend the incision if necessary.
Results The senior author has now completed more than 400 of the MIS QS surgeries since February of 2002. The procedure now requires approximately 50% more time than the standard TKA. The blood loss is 20% less, as measured by intraoperative and postoperative cell-saver collections and transfusions. The average length of stay has decreased by 2 days from the standard TKA. Pain scores, pain medicine require-
Figure 13 (A) The tibial sizing plate has 2 posterior hooks that can be deployed to reference the posterior cortex of the tibia on either the medial or lateral side, or both. (B) The handle for the tibial plate angles around the patellar tendon to avoid internally rotating the component while positioning the plate. (Color version of figure is available online.)
Figure 12 The knee is flexed to 70° and the finishing cuts are completed. (Color version of figure is available online.)
ments, and physical therapy participation have all improved in the quadriceps sparing TKA population when compared with the standard TKA. Greater ROM in the range of 20 to 30° has been measured for quadriceps sparing TKA, and this difference persists for at least 3 months. Postoperative alignment as determined radiographically has shown no statistically significant difference overall from matched controls un-
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ments, and time till participation in physical therapy while concurrently increasing early ROM.16,17 The findings have also shown Knee Society Scores and radiographic alignment outcomes that are comparable to standard TKAs without significantly increasing complications or compromising patient safety. The short-term results appear to be promising. Longterm results and clinical trials comparing the different MIS techniques will certainly need to be completed; however, there is little doubt that smaller exposures and limited arthrotomies will become more common in the next few years.
References
Figure 14 (A) The MIS tibial component has a shorter keel for ease of insertion. (B) A drop-down screw can be inserted through the tray. (Color version of figure is available online.)
dergoing standard TKA over the same time period and Knee Society Scores are the same in both populations. There are 3 tibial component loosenings, 1 early infection, 2 late infections, and 2 tibial components are in 7° of varus. Two of the tibial loosenings have been revised using a standard tibial tray with a stem. The early infected knee was removed and reimplanted with success. The 2 varus tibias have not required surgical correction. One of the late infections has been removed and reinserted and the other is pending further surgery.
Conclusions Minimally invasive TKAs are in the early stages of development and are improving in a step-wise fashion. The QS MIS TKA does not violate the extensor mechanism or the suprapatellar pouch. The early results have shown decreased blood loss, hospital stay, pain scores, pain medication require-
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