The Journal of Pakistan Orthopaedic Association
PRIMARY TOTAL KNEE REPLACEMENT. Masood Umer, Yasir J Sepah & Muhammad A Rehman
INTRODUCTION Over the past two decades total knee replacement (TKR) has become one of the most successful and cost effective treatment for alleviating knee pain and restoration of physical activity particularly in patients who do not respond to medical therapies. Variations in patient’s health status at the time of surgery, type of prosthesis and training of the orthopedic surgeon affects the overall outcome of the procedure. Further improvements in design are required in order to improve the functional outcome of the procedure. As more and more patients are undergoing this complex procedure in Pakistan, the technical details need to be highlighted for young surgeons and our postgraduate students. This article describes the surgical procedure of primary total knee replacement. Preparation of the limb The patient is placed supine on an ordinary operating table. Correct identification of the side to be operated is essential and marking it with permanent ink on the pre-operative rounds is recommended. This should be done over the knee joint rather than the foot and/or ankle as that mark gets hidden after draping. High placement of the tourniquet proximally into the thigh and groin is required, so as to prevent it from slipping down during the procedure [Figure 1b]. Patients having bulky
and ‘conical’ thighs should be recognized and the excessive subcutaneous folds should be pulled distally from the mid-thigh before application of the tourniquet in order to make them act as barriers against the tourniquet slipping down . A thick layer of cotton bandage under the tourniquet will not only reduce direct pressure on the skin but will a l s o p re v e n t b l i s t e r fo r m a t i o n . Circumferential bandaging of the tourniquet Velcro strap with a cotton bandage or an adhesive tape should be done to prevent snap opening of the Velcro during the procedure. An extra strip of adhesive tape between the distal end of the tourniquet and the lateral aspect of the loin may be required in very obese people [Figure 1b]. The foot is then prepared first with the appropriate antiseptic solution, wrapped in sterile stockinet [Figure 1c], and held by a surgical team member as another member paints the rest of the limb all the way up to the tourniquet. Standard draping is then performed with at least one waterproof drape going form below the leg over to the abdomen. Sufficient slack should be maintained in the drapes so as to allow easy and rapid flexion and extension of the knee joint during surgery. A foot stabilizing post can be kept at the level of the knee joint in order to support the foot in positions of knee flexion minimizing the amount of assistance required. The knee joint is then sealed with a waterproof adhesive
---------------------------------------------------Correspondance: Dr. Masood Umer Assistant Professor Department of Surgery Aga Khan University Hospital Karachi, Pakistan. Email:
[email protected] Phone: 92 21 4864760
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op-site from the proximal to the distal drapes. The op-site should be applied in maximal knee flexion. It is best to perform an examination under anesthesia before the draping, but it can be done now if not done till this time. The range of motion and the stability of the collateral ligaments and any flexion contractures should be carefully documented. The tourniquet is then inflated to at least double the systolic pressure. The use of esmarch bandage for exsanguination before putting the tourniquet on varies from surgeon to surgeon. The knee should always be maximally flexed before inflation in order to prevent quadriceps muscle being tucked under the tourniquet and to ensure freedom of motion intra-operatively . Also make sure that the scrub nurse has arranged her trolley and the diathermy and suction tubes are properly working before the inflation of the tourniquet, so as to minimize time wastage after inflation. One can now proceed with the skin incision. Skin incision: It is imperative for the beginner to mark the important landmarks and the incision on the op-site before tourniquet inflation. These include the outline of the patella, patellar tendon and the tibial tuberosity [Figure 1d].. The knowledge about previous scars is very important and even an experienced surgeon would like to plan and mark the new incision before starting. In this case the old scar is sometimes not visible under the Opsite and markings should always be made before application of the op-site. The standard skin incision is in the midline anteriorly, centered over the patella and extending distally and proximally to about 10cm in each direction. Distally, it passes August 2008
over the medial border of the patellar tendon and ends medial to the tibial tuberosity [Figure 1d, & e]. The proximal extent can be carried medially if a sub-vastus or a midvastus approach is being contemplated. This medial deviation is acceptable in varus knees, but may prove difficult and unwise in dealing with a valgus knee. A perfect midline incision would always appear to be laterally biased at the end of the surgery on a moderately varus knee, once correct valgus alignment is restored. Care should be taken to keep at least 2cm margin of skin from any previous incisions and avoid making flaps of less than 60 degrees wit h the old i ncisions. Alternatively, the same previous incision, provided it will not hamper your exposure, can be used. A previous transverse scar over the patella can safely be crossed at right angles. The incision is carried vertically down until you cut the fascia (scarpa’s fascia) overlying the quadriceps muscle, patella and the patellar tendon. It is important to recognize this layer of superficial fascia as it blends with the epimysium covering the vastus medialis proximally and the paratenon of the patellar tendon distally. There is a variable amount of fat beneath this fascia and the actual joint capsule. The medial skin flap is then raised below this fascia so as not to disturb the fasciocutaneous perforator vessels [Figure 2a]. The extent of this dissection is now dependent on which approach you want to follow. In a classical medial para-patellar approach you need to dissect about 1cm medial to the medial border of the patella. The lateral skin flap should not be disturbed at this point unless you want to do an extensive lateral release for a valgus knee.
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standard and most commonly used approach to enter the knee joint. The incision begins in the quadriceps tendon about 6-7 cm proximal to the superior pole of the patella leaving at least 5mm of tendon with the adjoining vastus medialis muscle . It then curves around the medial border of the patella leaving at least 5mm of cuff of soft tissue attached to the patella and then continues down medial to the patellar tendon. The original approach described by Insall comes straight down without the curve around the patella. The capsule is then raised subperiosteally from the surface of the medial half of the patell a in his approach. Mid-vastus and sub-vastus approach: These are alternate approaches popularized by surgeons who believe that going through the quads tendon undermines its strength and function. According to some, it leads to q ua dr i cep s i n hi b i t i on an d d e la y s rehabilitation . For the sub-vastus approach, the medial skin flap is dissected sub-facially all the way to the medial end of the vastus medialis muscle. The medial curved incision into the capsule around the patella is then carried around down to the adductor aponeurosis. The vastus medialis is then lifted off this aponeurosis and the medial inter-muscular septum by blunt dissection thus forming a continuous flap with the patella and the patellar tendon. This approach is in the anatomical plane and hence blood loss is minimal. It is quite difficult, however, to correct a valgus deformity with this approach . The mid-vastus approach is directed about 5cm into the substance of the vastus medialis muscle splitting it into two halves in the direction of its fibers. One or two occasional intramuscular bleeders may be encountered and must be cauterized as 132
they can cause considerable post-op hemorrhage. Joint debridement: The synovial fluid escapes readily as soon as the capsule is opened and it should be looked at to document any abnormal characteristics . Suspicious looking fluid should always be sent for gram staining, culture and sensitivity. The supra-patellar pouch is then cut opend, the patella everted, and the knee is now flexed. Cutting the patello-femoral ligament(s) facilitates the eversion of the patella [Figure 2d]. Flexing a primary stiff knee may not be easy and considerable adhesiolysis in the supra-patellar pouch and inside the joint along with release of the cruciates and collateral ligaments may be required before flexing the knee. This all should be executed very patiently in order to avoid avulsion of the patellar tendon from the tibial tuberosity. This is a dreadful, although very rare, complication in the case of a primary knee replacement. The joint should now be examined for the presence of synovial inflammation/hypertrophy and the presence of pseudogout deposits. Angry looking synovium and whitish deposits of pseudogout, which can be a source of postop pain, should now be excised. Excision of the supra-patellar fat pad is then done. A total or near-total excision is performed taking care not to injure the patellar tendon. This is best done by protecting the tendon with a retractor in the infra-patellar bursa and lifting the tendon above, hence, leaving all the fat suspended down which can then easily be cut. As much fat should be excised as is adequate to give you an exposure of the lateral tibial pleatue. P erio stea l refl ect io ns bet ween th e
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undersurface of the patellar tendon and the anterior tibial cortex can also be cut to improve the lateral tibial exposure. Some surgeons would argue that this fat may be a source of blood supply to the tendon and patell a and woul d t hus recommend i nco mpl et e o r mi ni mal e xci sio n . Grabbing it with a meniscus forceps pull it inwards and then excise the medial meniscus. It is then cut vertically in the interval between the meniscus and the meniscotibial or coronary ligaments. The incision is always from outside-in and not the other way around. As much meniscus is excised as is visible with a fully flexed knee and the rest can be excised later. The lateral meniscus is also excised in a similar fashion. It is important to find the inferior lateral geniculate artery below the lateral meniscus and cauterize it at this time. The cruciate ligaments are then excised. It may be difficult to excise the PCL completely at this stage. The femoral insertion is easily detachable and the tibial origin should be left for a later period. Anteromedial soft tissue release is now performed. The medial capsule and the coronary ligaments are peeled off the anteromedial tibial cortex by sharp subperiosteal dissection. This dissection is then carried medially to include the superficial and the deep medial collateral ligaments. Their structural continuity and distal attachment to the tibial periosteum is carefully maintained. The pes tendons may or may not be released depending on the initial varus deformity. The dissect ion is carried posteromedially so as to bare the medial borders of the tibial plateau taking care not t o cut th e a tt ach ment of t h e semimembranosus muscle. We can now proceed to our bony cuts. August 2008
Bone cuts: Sequence of the bone cuts depends upon the philosophy or school of thought that one follows. First and the most widely used is the gap technique, which is the usual practice of people who use a cruciate substituting prosthesis. In this technique, the tibial cut is made first and then the flexion and extension gaps are equalized by sequential soft tissue release. The final chamfer femoral cuts are made only once you get equal size spacers in the flexion and extension positions. Second is that of joint line theory, where the emphasis is more on preserving the joint line and is preferred by people who want to retain the PC ligament. Here all the bony cuts are made first and the soft tissue balancing done later. The most adequate spacer that fits does the joint line maintenance. The senior author has had extensive exposure to both these techniques; the joint line techniq ue is bei ng described here. The femur is cut first. Before starting, the entire anterior femur from the medial to the lateral side is denuded of the fat and periosteum. This is important while drilling the medullary cavity as you can gauge the center of the cavity with one hand grasping the anterior femur. The entry hole, made with a punch, is located 5mm anterior to the intercondylar groove in the midline . The 8mm drill hole is then used to access the medullary cavity. The surgeon should make sure that he/she drills the entire length of the drill bit and does not strike the anterior or posterior cortex while drilling. All the fat and marrow in the medullary canal is then su cked out b efo re in troduc ing t he intramedullary alignment rod. Using the big rod gives a good intramedullary fit making
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it easier to make accurate antero-posterior cuts. Sometimes due to deformity and excessive curvature a shorter rod has to be used, but this has the disadvantage of toggling and hence the possibility of making inaccurate antero-posterior cuts. Next thing of vital importance is to produce some (about 3-5 degrees) external rotation of this intra-medullary alignment guide [Figure 3a]. This is important for two reasons; firstly, to produce a rectangular rather than a trapezoidal flexion gap and to improve patellar tracking. An internally rotated femoral component will have higher chances of patellar subluxation, dislocation and clunking. The best way to ensure external rotation is to make the alignment rod and jig parallel to the transepicondylar axis. This is an imaginary line connecting the lateral to middle of the medial epicondyle. The other method is to make it parallel to the curt surface of the tibia. The jig is now pinned to the distal femur in correct rotation. The anterior cutting jig is now fixed with this jig and the free proximal end of this jig is placed on the most prominent aspect of the antero-lateral cortex and the whole jig is allowed to settle inside the original jig. Both the screws of the top jig are then tightened and a cut is made through the slots. Before making the cuts it is always better to check the depth of the cut by the runner blade/Miller guide in order to make sure that the saw does not notch the anterior femoral cortex [Figure 3d & e]. This notching can act as a stress riser and a potential for future peri-prosthetic fractures. The anterior femur is then cut and excised . The anterior cutting jig is then replaced by the distal cutting jig. One must make sure that the side of the knee 134
is the same as the side printed on the top of the jig. As this cut is perpendicular to the mechanical axis of the femur, this jig is fixed at the pre-determined valgus angle [Figure 4a]. This angle should be determined preoperatively on all patients and is usually between 4-7 degrees. The jig is then fixed with pins and the distal cut is made. Next step is that of measuring the anteroposterior diameter of the distal femur. The inferior surface of the measuring device should be flush with the posterior condyles. If the measurement is in between the two sizes, the one closer is selected. If the measurement falls in the middle then the smaller size is chosen. The antero-posterior cutting jig is now placed over the distal cut surface. One should make sure that the overhang of this jig rests flush with the anterior cut surface of the femur. It is also important to protect the collateral ligaments at this stage by appropriate ligament retractors. The posterior cuts are made first. It is important to exercise good control and stop the saw as soon as the condyle is cut, otherwise one can cut important soft tissue structures behind the knee. If the jig is placed in the correct external rotation then the medial condyle is always cut more than the lateral condyle. The chamfer jig is now placed on the femur making sure it is properly seated flush with the anterior and distal cortex. Its placement has to be central. Some surgeons would make it flush with the lateral cortex of the femur. A central position with equal bone on the medial and lateral cortices is preferred. The chamfer cuts are then made followed by the cut on the intercondylar notch. A smaller saw then cuts the bone for the notch.
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Any posterior osteophytes, loose bodies, remnants of the menisci and the proximal portion of the PCL are now excised. Particularly, osteophytes from the inferior portion of the notch are carefully excised so as to prevent impedance to the insertion of the trial prosthesis. The tibia is now cut at a distance of 8-10 mm form the less involved side [Figure 5a]. The whole of the tibia is brought forward anteriorly by a Hohman retractor placed in the notch of the resected PCL. The extramedullary alignment rod is applied flush with the shin and kept vertical. The patellar tendon is retracted laterally and the depth of the cut checked with a runner blade. The tibia is then cut and the bone excised. The tibial cutting jig has an in-built 3 degrees of posterior slope and this can be increased to varying degrees depending on the system being used and personal choices. The tibial template is then positioned making sure that it is flush with the posterior cortex and also not overhanging anterior-laterally. The center of the jig is kept at the level of the medial third of the tibial tuberosity. The tibial hole is now created. It is better to remove the superior 1cm square of bone with an osteotome first and then use the peg. The peg is driven down to the required level and then removed [Figure 5b]. The patella is then cut in the end [Figure 5d]. A lot of surgeons are now moving away from routine patellar re-surfacing during primary TKR. This is being described here for those who still prefer to replace it. The patella is everted and the synovium surrounding the patella is excised. Soft tissues a ro u n d t he p a t e l l a ar e r el e a se d August 2008
circumferentially so as to expose enough bone for the patellar clamp to grasp . The thickness of the patella is then measured by a vernier caliper . This is done to resect about 10mm of bone from its articulating surface and then patellar height is rechecked with the trial implant. The aim being that both the measurements should be equal, eliminating any possibility of making the patella thick after surgery. The hole guide is then placed over the cut surface with a slight medial bias. The holes are made with the drill and the trial implant put in to confirm the correct depth of the hole. Trial reduction: Insertion of the trial prosthesis is now done. Make sure that the femoral component is not flexed and should be flush with the distal cut. It is important to control the rotation of the tibial tray to the pre-determined mark on the anterior cortex of the tibia. Reduction of the joint is now done with progressively increasing sizes of the polyethylene inserts and the medio-lateral and antero-posterior stability checked. The stability is checked in both extension and flexion . One to two mm laxities on the medial and lateral sides and complete extension is the aim. The trial insert size, which suits the above criteria best, is then selected. The patellar tracking is then checked with the ‘no thumb’ rule and the need for any lateral release assessed. If the patella seems to be subluxating or dislocating laterally, a lateral retinacular release from the undersurface is performed. This release is best performed about 5-10mm away for the margin of the patella. The release is done sequentially and the tracking checked
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repeatedly so as not to overdo it. When an extensive release is required the superior lateral geniculate artery is dissected and should be carefully spared. The patella should be able to track smoothly in the groove after the release. The bone is now ready for cementation. Cementation The gold standard for fixation in total knee arthroplasty remains t o be cement . The joint and the bone ends are washed with normal saline, preferably with a pulsatile lavage system. This is to remove any clots, marrow and fat debris for the cut bone ends. The joint is also washed thoroughly to remove any clots and debris. The bone surfaces are now dried as one of the team members mixes the cement. For an experienced team one batch of cement is enough to implant all the three components. The Intramedullary femoral hole is also now plugged with a small piece of cancellous bone to prevent any post-op bleeding form the medullary cavity. Cementation of the femur is done first. Cement is carefully applied to the posterior condyles and the anterior flange of the implant before hammering it on the femur. Adequate seating of the implant should be confirmed form both sides and the excess cement removed after cutting with a sharp knife. All the cement present in the intercondylar notch area should also be removed. Next, the tibial surface is brought anteriorly with a Hohman retractor and the tibial implant put in after applying cement on the undersurface of the base plate. Some cement is also applied on the walls of the peg hole. The rotation of the tibial implant is carefully controlled during insertion. The last bit is 136
usually hammered in and again the excess cement removed from the sides by a curette or a knife. The joint is then quickly reduced with a trial tibial insert and held in full extension by putting a roll under the ankle joint. The patellar bone is now cemented in a similar fashion and all the extra cement around the implant is also removed . The patellar clamp is applied until the cement is hard. The joint is held in full extension until the cement is rock hard, which usually takes about 10 - 13 minutes. The tourniquet can now be taken down and hemostasis secured. The joint is again washed and the trial tibial plastic is replaced by the actual plastic insert of the pre-determined size and secured with its locking key . Closure: A drain is now put inside the joint and the tip is brought out supero-laterally . If there are no further bleeders the joint is ready for closure. The capsule is closed with interrupted 1/0 Vicryl suture taking care not to take the drain in your stitches. The subcutaneous layer including the superficial fascia is stitched with 2/0 Vicryl, again with interrupted sutures. In an obese person a second sub-cutaneous layer may also be required. The skin is stitched with staples or subcuticular prolene. Antiseptic dressing with a lot of cotton wool to absorb any leaking hematoma is then performed. To avoid any complications in morbidly obese patients extra care should be taken in softtissue closure and protection of the medial collateral ligament, where necessary.
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FIGURE-1
FIGURE-2
FIGURE-2
FIGURE-3
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FIGURES WITH LEGENDS:
FIGURE 4
FIGURE 1
Final shape of the distal femur
Preparation of lower limb
After correct placement of the distal femoral cutting jig the intramedullary rod is removed and distal femur is cut (a), (b). Chamfer cutting jig is now centrally placed on the distal femur (c); chamfer cuts and notch are created (d).
Correct application of the drapes (a), tourniquet (b) and stockinet (c). The incision and the landmarks (d) are drawn after the application of op-site. The incision is midline above the patella and ends medial to the patellar tendon and tibial tubercle (e) FIGURE 2 Deep dissection After making the skin and subcutaneous incision a medial para patellar arthrotomy (a) is done. Sub periosteal release of the joint capsule (b) and deep medial collateral ligament (c) is done over the proximal tibia. Patella is then everted and femoral central hole made (d).
FIGURE 5 Proximal tibial cuts and use of spacer Proximal tibial cutting jig is placed about 10mm below the less involved side (a). Cut is made after confirming it with a runner blade (b). The tibial spacer is now inserted in increasing sizes until correct ligament balance in flexion and extension is achieved (c). Patellar cut is then made (d).
FIGURE 3 Distal femoral cuts After inserting the intra medullary guide distal femoral resection jig is inserted inabout 3-5 degrees of external rotation (a) and fixed with pins (b). The correct valgus angle and side are confirmed at this point (c). A runner blade is used to check notching of the anterior cortex (c) and to avoid cutting the collateral ligaments (d). FIGURE-5 138
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deformity. Five to fourteen-year followup. J Bone Joint Surg Am 2004, 86A(12):2671-2676.
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arthroplasty. A prospective, randomized, double-blind study with five to seven years of follow-up. J Bone Joint Surg Am 20 01 , 8 3-A(9): 13 76 -1 38 1. 15. Barrack RL, Wolfe MW: Patellar resurfacing in total knee arthroplasty. J Am Acad Orthop Surg 2000, 8(2):7582. 16. Hsu RW: The management of the patella in total knee arthroplasty. Chang Gung Med J 2006, 29(5):448-457. 17. Hofmann AA, Goldberg TD, Tanner AM, Cook TM: Surface cementation of stemmed tibial components in primary total knee arthroplasty: minimum 5year follow-up. J Arthroplasty 2006, 21(3):353-357. 18. Helmers S, Sharkey PF, McGuigan FX: Efficacy of irrigation for removal of particulate debris after cemented total knee arthroplasty. J Arthroplasty 1999, 14(5):549-552. 19. Emerson RH, Jr., Ayers C, Higgins LL: Su rgi cal clo sing in t ot al k nee arthroplasty. A series followup. Clin Orthop Relat Res 1999(368):176-181. 20. Beer KJ, Lombardi AV, Jr., Mallory TH, Vaughn BK: The efficacy of suction drains aft er ro uti ne t otal j oin t arthroplasty. J Bone Joint Surg Am 1991, 73(4):584-587. 21. Insall JN: Infection in total knee arthroplasty. Instr Course Lect 1982, 31:42-48. 140
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