Hybrid Surgical Technique in Total Knee Replacement

Abstract

Hybrid surgical technique for total knee arthroplasty (TKA) combines the gap balancing and measured resection techniques to achieve a well-balanced knee both anatomically and kinematically. It preserves bone, respects the soft tissue and provides better patellofemoral alignment. The techniques work with the same instrumentation as required for measured resection hence do not add to inventory. In addition, the technique imparts a better understanding of the intricacies of the knee alignment and the role of ligaments to the trainees and surgeons at the beginning of careers. These techniques help surgeons to manage complex cases with attenuated ligaments or moderate bone loss. This understanding of bony alignment principles and ligaments helps easy transition and understanding towards the application of navigational or robotic surgical dictum.

1. Introduction

Total knee arthroplasty has evolved over time from the time of Dr. Walldius [1] who used a hinged design for knee arthroplasty in the 1950. After this pioneering work, Dr. John Insall and his team painstakingly developed the art of knee arthroplasty which is now considered amongst the most successful and as common orthopaedic procedures, changing the lives of millions of people.

Dr. John Insall, Dr. Peter Walker, Dr. Albert Burstein and Dr. Ranawat [2, 3] introduced total condylar prosthesis, principles of which lead to the development of measured resection techniques (using mechanical limb alignment) which have evolved since its introduction in 1970, the technique has been refined and improved over the years with advancements in understanding, surgical tools and prosthetic designs [4].

Later, the surgeons started to discuss the importance of ligament and soft tissue balance, an era of debate from 1980 onward leading to the introduction of gap balancing techniques that focus on achieving symmetrical flexion and extension gaps through ligament releases and bone resections for better stability, motion and longevity. The seminal work by Laskin [5] in the 1980s and 1990s, among others, emphasized the importance of ligamentous balance and how it contributes to the success and longevity of total knee arthroplasty (TKA).

On the other hand, surgical approaches like minimally invasive surgery (MIS) or quadriceps-sparing TKA were introduced. The implants evolved to patient specific TKA, and multi-curvature diameters of femoral implants. The tibial polyethylene quality improved to produce less wear, conforming or mobile and now the medial pivot design featuring a conforming medial compartment in the sagittal and frontal planes creating a shallow, “ball and socket” joint is developed. Uni-compartmental knee arthroplasty replacement is another endeavour to improve function and increase longevity.

The quest to improve the art of TKA continued and later computer-assisted surgery (CAS) or navigation-based total knee arthroplasty (TKA) was introduced in the late 1990s and early 2000s. This technology was developed to improve the accuracy and precision of component positioning and alignment in TKA, aiming to optimize outcomes and implant longevity [6]. Dr. Werner Siebert and Dr. Alfred Stiehl from Germany, sparked the idea of using fluoroscopy, later more dedicated systems for computer navigation in TKA began to emerge [7].

Finally, robotic-assisted total knee arthroplasty (TKA) evolved from the work of Bargar WL, Bauer A and Börner M, using the ROBODOC system, initially focused on total hip arthroplasty but later expanded to include TKA with the first TKA in late 1990 [8].

The robotic arm-assisted surgery which is the latest vogue, aims to preserve and customize the bone and ligaments resection to individual anatomy with an aim to achieving a state where the knee functions as near to natural function and longevity of prosthesis increases.

The journey and developments continue in all aspects of TKA, at times some previous concepts arise on the surface while at others some new one’s face failure.

Given the above history of evolution, the basic principles introduced in the early part of the journey of TKA are still the mainstay of understanding the art of TKA, these principles even help in understanding the principles of the most modern robotic techniques. Hence a thorough understanding of these principles and their applicability from the core competency to performing total knee arthroplasty is essential. In addition, not all hospitals or health systems of individual countries can offer the most advanced equipment (which translates to expensive) for knee arthroplasty to the public.

The trainees/fellows, who are the future surgeons and inventors need to understand the core knowledge to be able to catch up with current and develop new ideas that improve the basic concepts.

All in all, the advancement from past to future in the development of knee arthroplasty has had one objective only, to develop a knee arthroplasty that achieves a perfect harmony between bone cuts, ligament and soft tissue balance, implant rotation, static and dynamic balance of knee stability and function that results in a happy patient, albeit despite all these advances 20% of TKA patients are unhappy with well-fixed Knee [9].

In this chapter, we will focus on knee replacement technique that endeavour to reach the goals of a good arthroplasty, easy to teach to trainees and provides a core understanding of technicalities of TKA to novices and abecedarian (arthroplasty surgeons at the beginning of the career).

The two most widely surgical methods/techniques for THA are the measured resection technique and gap balance technique.

These techniques have been described previously in this book and in the literature pros and cons have been discussed extensively.

We adopted a different method to the ones described in the literature to combine these techniques.

A summary of the main principles and major strengths and weaknesses of these techniques are described here.

Both these techniques aim to achieve correct femoral component rotation which in turn affects patellofemoral tracking, tibial component rotation and soft tissue tension required for stability in flexion and extension using mechanical alignment of tibia and femur.

2. GAP balancing

Gap balancing techniques require ligamentous releases before bone cuts are performed. These releases correct fixed deformities and return the limb to the correct alignment [10, 11].

There are two ways, either (1) balancing extension or (2) creating a flexion gap can be performed first.

The most used technique balancing in extension is performed first.

Hence after initial dissection (surgical approach) usual medial release of deep medial collateral ligament (dMCL) is performed. The distal femoral resection is performed between 3° and 7° of valgus followed by the proximal tibial cut made exactly perpendicular to its mechanical axis using appropriate guides. All osteophytes are then removed from the tibial plateau and the posterior aspects of the femoral condyles (Figure 1a–c).

Figure 1.

a) Distal femoral cut assessment with easy fall of angle wing. Also note marked Transepicondylar axis. b) Extra medullary tibial alignment guide. c) Tibial cut after distal femoral cut.

Then, laminar spreaders or tensioning devices are used to distract the gap and allow access for the removal of posterior (medial and lateral) osteophytes (Figure 2a and b).

Figure 2.

a) Gap assessment tool. Triathlon® Stryker Knee System. b) Gap assessment in situ for extension gap check. Triathlon® Stryker Knee System.

Once all the osteophytes have been removed, attention is diverted to tight ligamentous structures and sequential releases are performed in extension until neutral limb alignment and a symmetric extension gap is achieved. The flexion gap is then created in 90° of flexion, similar to the extension gap, removal of osteophytes and then ligament release to achieve a rectangular gap, equal to the extension gap (Figure 3a and b). Then by applying the femoral cutting block 1 × 4 (after sizing) setting the rotation of the femoral component based upon gaps and tibial surface., starting with posterior condyles, the anterior and chamfer cuts are made.

Figure 3.

a) Flexion gap. b) Flexion gap balancing device in use GENESIS II© System/Smith & Nephew.

However, some surgeons balance the flexion first, and the principles of gap balancing remain the same with some changes in the sequence of steps. After the initial dissection, the tibial cut is performed first, knee flexed to 90°, tensioning the flexion gap with laminar spreaders or tensioners, thorough removal of osteophytes then addressing the ligaments, achieving the rectangular flexion. Then femur resection guide is used to perform posterior condylar and distal femoral cuts are performed and the flexion gap is measured. The knee is extended, and an extension gap (using laminar spreaders/tensioners) is created which is equal to the flexion gap. The anterior and chamfer resections are made.

3. Disadvantages of gap balanced

1. Tibial cut has to be accurate; varus or valgus cut can lead to internal and external rotations respectively.

2. Complete osteophytes removal is necessary before ligament/soft tissue release. Failure to release osteophytes before soft-tissue release can lead to rotational optimization and imbalance/asymmetry between flexion/extension gaps after final bony cuts.

3. Sometimes to release posterior osteophytes one must perform initial skim cuts of posterior condyles to be able to reach the osteophytes.

4. When using posterior stabilized TKA implants, resection of PCL may result in a larger flexion gap than the previously balanced gaps.

5. Balancing flexion and extension can potentially raise the joint line leading to patellofemoral tracking issues (pain/fracture). Every 1 cm of joint line elevation increases patellofemoral contact forces by 60% [12].

6. Balancing the knee in extension does not automatically result in balance in flexion, especially in valgus knees, as iliotibial band release effects widen the extension gap, while popliteus release results in the widening of the flexion gap.

7. In severe varus or valgus deformities, the collaterals are attenuated, tensioning during flexion gap, when there is attenuation of superficial the medial collateral ligament can result in an asymmetric and excessive medial flexion space leading to an internally rotated femoral component.

8. Osteophytes removal is paramount for tissue tensioning and balance, if all osteophytes are not removed and bone cuts are made, it can cause changes in flexion or extension gap balance.

4. When not to use gap balancing

Firstly, collateral integrity should be present, or rotational errors could occur [13].

Secondly, if non-reduceable, fixed deformities are found in a patient then gap balancing may not be the appropriate choice as it hampers correct bone cuts and component positioning [14].

5. Measured resection

Measured philosophy is the conjunctional use of bony landmarks to determine femoral component rotation [12]. In contrast to gap balancing, here bone cuts are made before soft tissue balance.

The surgeon replaces bony resections with a prosthesis of matched thickness and determines femoral implant rotation using anatomic landmarks to maintain the joint line, restore posterior condylar offset and optimize joint kinematics and alignment [15].

Generally, three bony landmarks used are, Transepicondylar Axis (TEA) (surgical and anatomical); Anteroposterior Axis (AP) (Whiteside’s line) and Posterior Condylar Axis (PCA). These axes are to be used in combination, as individual variations in anatomy and/or deformity can alter the femoral component placement. These landmarks have been defined previously in this book.

The success of measured resection also hinges on a surgeons’ ability to accurately identify these landmarks intraoperatively. For example, Jerosch et al. showed that when surgeons had to mark the epicondyles in experimental conditions, the medial side position varied by 22.3 mm and the lateral side varied by 13.8 mm [16, 17]. When it comes to identifying anatomical landmarks, Philipp von Roth points out that, “identification can be difficult and even if clearly identifiable, the landmarks show a large anatomical variance”.

Even if anatomical landmarks are easy to identify in many routine TKA, Abdel reminds us that, “This can lead to flexion and extension gaps that are not initially balanced, as well as variations between the medial and lateral side, in regard to stability, that require additional soft-tissue releases”.

In the technique, the tibial and femoral resections are performed independently of each other, so the sequence of resection does not matter. However, usually after the initial surgical approach and soft tissue dissection, the distal femoral resection is performed to achieve a neutral mechanical axis, set for 5–7° of anatomic valgus using the intramedullary rod and appropriate cutting guide defined by the system being used (Figure 4a–c). Then the femoral sizing is performed, and the use of 1 × 4 block, which most often references the posterior condylar axis (the anterior referencing can be used depending upon the type of system used) for AP positioning of the cutting jig the anteroposterior (AP) and chamfer femoral resections are made parallel to the TEA or/and perpendicular to the AP axis (Whiteside’s Line) to achieve appropriate femoral implant rotation. The cutting 1 × 4 block jig has built-in 3° of external rotation by virtue of allowing thicker distal medial and posteromedial bone resections compared to distal lateral and posterolateral bone resections. This difference in resection thickness results in net femoral implant external rotation and a decrease in the normal femoral anatomic valgus that corresponds with the loss of tibial varus through a perpendicular tibial resection [14, 18].

Figure 4.

a) Assessment road holder (a metallic rectangular object in many TKA sets). b) The instrument is utilized to guide the rotational femoral cuts (femoral rotation) based upon tibial cut. Triathlon® Stryker Knee System. c) The instrument is utilized to guide the rotational femoral cuts (femoral rotation) based upon tibial cut. GENESIS II© System/Smith & Nephew.

The next step is to perform tibial resection, a neutral or 90° tibial resection to the anatomical axis of the tibia (this results in more bone resection laterally than medially). Tibia is not sized at this stage.

Once the bony resections have been performed, osteophytes are meticulously removed from both the femur and the tibia. Trial implants are placed, and knee stability is tested throughout a complete ROM, if necessary, ligament releases are performed later in the procedure to achieve balance [19].

6. Disadvantages of measured resection

1. Measured resection technique uses the landmarks to set femoral rotation at the expense of joint congruity.

2. These landmarks have substantial variation in femoral anatomy from patient to patient, resulting in considerable variability of femoral implant rotation.

3. Rotational errors can occur due to anatomical or inter-surgeon variability to define the three landmarks, especially the posterior condylar axis is considered the least reliable anatomic landmark to set the amount of femoral implant external rotation. This is particularly true in the valgus knee where the lateral femoral condyle is often hypoplastic [20, 21, 22].

4. The disadvantage of measured resection is mismatch of flexion and extension gaps. It is difficult to perform objectively soft tissue releases to balance gaps. Releasing ligaments after setting the flexion gap based on bony landmarks can disrupt the symmetry of the flexion gap. A good example is releasing the tight medial side of a knee in extension which can create laxity and asymmetry in flexion [23].

5. Another issue with the technique is an increased incidence of coronal instability. In a biomechanical study an increased incidence and magnitude of femoral condylar liftoff at zero degrees, 30, 60 and 90 of flexion with measured resection compared with gap balancing. However clinically despite slightly worse joint symmetry in measured resection compared to gap balancing there was no difference in function or quality of life [12, 16, 24].

Having discussed both the gap balance and measured resection techniques and pointing out potential pitfalls, we tried to adopt a middle way, where we take the strong points of both techniques, remaining wary of the possibilities of errors. This is the hybrid surgical technique, which we have been using in our institution since 2018. A total of 100–150 arthroplasties per year, single surgeon, posterior stabilized knee, posterior referencing implants Triathlon® Knee System (Stryker, Michigan, U.S.) and anterior referencing using Genesis II (Smith & Nephew; Memphis, Tenn. U.S.) (PS). It is a short-term result, but we have 99.9% patient satisfaction and no revision rate for any reason.

7. Our hybrid technique

1. Patient supine on the table, two footrests, one keeps the knee at 90° and the other holds the knee at maximum flexion.

2. Pre-operative intravenous antibiotic + intravenous tranexamic acid 1000 g.

3. Urinary catheter insertion/spinal anaesthesia/standard thigh tourniquet, inflated 90–100 mm Hg above systolic blood pressure.

4. The leg is marked to identify the bony landmarks at the knee. Gerdy’s tubercle, patella, patellar tendon outline and tibial tuberosity. Lower down we mark the tibial crest, malleoli with a midpoint of the ankle, middle of talus, extensor halluces longus tendon (EHL) and second metatarsal. All the midline points are joined (except Gerdy’s tubercle) starting from mid-thigh for incision, using a permanent marker (we palpate the tibialis anterior tendon, just lateral to it is extensor halluces longus (EHL) to identify the centre of talus [24]) (Figure 5a–c).

5. The leg is washed with 4% chlorhexidine/soap solution from proximal to distal.

6. After preparing the leg meticulously with betadine and alcoholic solution (it is left to dry), total knee replacement orthopaedic surgical drape pack is used and after a gentle single dabbing of skin creases with a swab, 3M™ Ioban 2™ antimicrobial incise drapes are applied on the leg. The anterior drape rape is applied in flexion and posterior in extension.

7. Landmarks and markings are rechecked as an application of Ioban can stretch the skin altering the markings (Figure 5a).

8. Midline incision, paratenon is preserved to remain attached to skin incision and subcutaneous tissue to preserve the blood supply and aid in closure.

9. Upper and lower borders of the patella are marked to assess the joint line at the time of closure. In addition, the dissection line from the quadriceps tendon, curving around the patella to the tibial tuberosity is marked to keep enough cuff of tendon for closure (Figure 5c).

10. Medial parapatellar arthrotomy performed as mapped.

11. The patella is everted or laterally subluxated without eversion depending upon tissue tension.

12. Soft tissue dissection like synovium, patellar fat pad and medial meniscus including subperiosteal medial release.

13. Grossly large osteophytes at the femur were removed and the lateral femoral cortex was cleared for later resections.

14. At this stage we draw the anteroposterior (AP) axis (Whiteside’s Line + Sulcus line combination) + Trans epicondylar axis TEA, a line that connects the prominence of the lateral epicondyle to the sulcus of the medial epicondylar prominence (site of the deep MCL fibres) (Figure 6a and b).

15. We define the femoral notch, if need osteotomies the osteophytes at the notch to identify the posterior cruciate ligament insertion, mark a point 9–10 mm above its insertion and just medial to midline for intramedullary femoral canal entry.

16. We insert the intramedullary rod and attach the femoral alignment guide for the appropriate side knee, dialled from 5–7 valgus (Valgus Cut Angle), from premeasured long films.

17. (A) We then attach the cutting guide, before the cut we insert the instrument “angle wing/comma guide” through the cutting slot, if it goes easily, this indicates an adequate cut. The cutting jig provides a thickness of 8–10 mm bone cut depending upon the manufacturer of the implants. (B) In the anterior cut first design, after insertion of the femoral intramedullary guide, we attach appropriate cutting blocks to make an anterior cut first and then attach a distal femoral cutting guide to cut the distal femur.

18. Then we draw our attention to the tibia, the necessary soft tissue dissection to remove the menisci, the cruciate from the notch.

    1. Care is taken not to damage medial or lateral structures capsule/ligaments, we cut outside-in, i.e., leave a sliver of the meniscus with the soft tissue on either side.

    2. Tibia is subluxed anteriorly, held with a double-prong retractor levering on the femoral notch.

    3. Popliteus is identified for protection later.

    4. Any major osteophytes identified at this stage were removed without removing proximal tibial margins when removing the osteophytes.

    5. The Hohmann retractor helps with the tissues to be kept away.

19. Extra medullary, tibial guide (extramedullary referencing alignment) is used (invariably), it is aligned with the marking of the tibial crest, central ankle, talus, EHL tendon and second metatarsal.

20. The tibial jig is checked to be parallel to the tibia in coronal and sagittal planes, aligned to the marks. Roughly east two fingers at the ankle and tight or one finger at the top helps.

    On the tibia we have three landmarks to place the long keel of the extramedullary referencing alignment these points being; (a) the medial third of tibial spines, (b) the lateral border of the patellar tendon (c) centre of the tibial plateau. These three are marked and then joined. Visually we align them to centre of the femoral notch and PCL insertion on tibia.

21. Once satisfied that the extramedullary referencing alignment guide is parallel to the axis (mechanical) of the tibia, then using the cutting guide we take 2 mm from the worst part (deepest) of the worn side (in varus knee medial side). However, we recheck the depth on the lateral side where 9 mm (implant thickness) is taken off the tibia. The few seconds required to do so is important in avoiding the excessive proximal tibial cut that becomes a problem for placement of the tibial plate. In addition we also check the thickness of tibial cut using “angle-wing” (Figure 7).

    If we want to conserve bone cut, we can cut from the top of the cutting block rather than from the slot. Rarely we had to reposition the cutting block to cut less or more bone if necessary.

    At times the tibial bone surface is very sclerotic (marble bone), the saw bends and cuts over the sclerotic area, resulting in an uneven cut.

    We first furrow and then drill the sclerotic area and redo the cut.

22. Having performed the cut, we measure it to see the accuracy of the templating done preoperatively. All these checks ensure the tibial cut is 90° parallel to the tibial axis.

23. Then we remove the extramedullary referencing alignment guide and extend the knee (Figure 6b).

    First manual assessment and visualizing the gap difference between medial and lateral sides.

    If the medial side is tight we assess the extent of medial release (which in fact is the release of deep MCL), and extend it further to midcoronal tibial, removal of medial osteophytes (tibia and femur) is performed, more often than not these steps solve the problem.

    Note: If manual inspection shows a very tight gap on both lateral and medial sides, then see if the knee had preoperative fixed flexion deformity and the distal femoral cut check with angle -wing was tight, we resect distal femur by 2 mm (Figure 6b).

24. After the initial measures of medial release extension passed the midcoronal tibia and removal of osteophytes, if the medial gap is still tight, we proceed to release the posteromedial corner (posterior oblique ligament), we insert the spacer block, (Note: no laminar spreaders, if still tight).

    1. If the spacer block cannot be inserted, we further the medial release distally to the direct head of the semimembranosus and proximally on the femoral side to the posterior capsule.

    2. If the spacer block goes halfway and does not go fully inside on the medial side. This shows most posterior tissues are tight. We then wait for femoral resection and removal of posterior osteophytes in the femur and tibia, posterior medial femoral capsular release and reassess the gap again. Keeping in mind to keep the popliteus intact laterally.

    3. After the femoral cut, we use a spacer block to check the flexion gap, it could be rectangular or might be tight on the medial side.

    4. Then we revert back to extension gap and the spacer block sits well in extension and flexion: the issue is resolved.

    5. However, if it is still tight in flexion and extension and the lateral side is fine (this happens in severe varus knees), then we prefer femoral origin release of the medial collateral ligament (FORM) [25, 26].

    6. With the knee flexed, the FORM is initiated with the identification of femoral attachment of MCL palpating the taut structure, over the medial epicondyle and medial sulcus in the AP direction.

    7. Sequential pie crusting, can be done in three stages, every stage is followed by a gap assessment with the spacer block, starting from the posterior most one-third of superficial MCL in stage one followed by gap assessment one can proceed to the anterior part.

    Even with the complete FORM, superficial fibrous strands attached to the femoral attachment site of the MCL are preserved to promote postoperative soft tissue healing.

25. In moderate varus, the gap is usually balanced before the FORM stage [26].

26. Then we proceed to femoral sizing and use of a 4 × 1 cutting block, make the appropriate cuts (anterior/posterior/chamfer cuts).

27. Check the flexion gap with the spacer block.

    Here the difference is that we do not use laminar spreaders, rather we use the spacer blocks which require gentle forces to assess the gap. Laminar spreaders stretch the ligaments with a force that can be quantified hence affecting the properties of creep/stress relaxation in ligaments.

28. In step 26; when the extension gap is balanced, in our hybrid technique we can set or more correctly will be able to substantiate the built-in 3° of external rotation of the femoral cutting block for rotational alignment. Simple use of any rectangular block from the set, placed on the tibial service and applying the femoral cutting block on its service will a set femoral rotation in relation to the tibia (Figure 4a–c).

29. Once all the cuts are made, the tibia is sized, trial components are placed and trial polyethylene is inserted to check the medialolateral stability in flexion and extension. We bring the knee to flexion/extension range of motion, to look for the following (a-b).

    1. Condylar lift-off throughout flexion to extension+ patella tracking without thumb.

    2. Still refinements/adjustments can be made in bony cuts and ligaments if needed. The functional word is minor.

30. Once happy, the original implants are cement.

31. While waiting for the cement to settle we inject a mixture of steroid + local analgesia + tranexamic acid in the tissues and posterior capsule.

32. The last thing is the insertion of polyethylene and the final check for stability, condylar lift-off and patellar tracking.

33. We give another dose of tranexamic acid at this stage before the release of torniquet.

34. Wash and close in layers and skin closed subcuticular. Mepilex® Border Post-Op dressing (Mölnlycke)

35. The dressing is untouched for 14 days if remains dry or unsoiled.

36. Adductor canal + genicular canal nerve block is done using ultrasound guidance by the anaesthesiologist+ intravenous PCA (patient control analgesia) started for 36 h.

37. No opiates or NSAID analgesia to the patient in post-operative period or taken home.

Figure 5.

a) Initial marking and use of Ioban (3M). b) Foot is also covered with Ioban to see the markings. c) Marking for medial patellar approach incision (vertical marking) and patella height (horizontal marking) for joint line assessment at closure. Note: 3M Ioban Sterile Antimicrobial Incise Surgical Drape.

Figure 6.

a) Marked Transepicondylar axis (note difference in the height between medial and lateral sides). b) Reassessing the Transepicondylar axis after distal femoral cut.

Figure 7.

Angle wings.

In our hybrid technique, we used the best features of both the gap balance and measured resection techniques with slight modifications based upon evidence-based medical knowledge and experience.

We used measured resection cutting block, taking advantage of technology that evolved from vast laboratory and clinical experimentation and applied time-tested basic principles embedded in developing the gap balancing techniques. This allowed us to avoid the pitfalls and best use of salient features of both technologies.