Technical challenges in revision total knee arthroplasty

Abstract

The number of revision total knee arthroplasty procedures is on the increase, and the modern-day arthroplasty surgeon must be equipped to deal with this growing challenge. Every revision can differ, in terms of the technical challenges encountered. These can include issues with exposure, joint line reconstruction, as well as bone loss and ligament deficiency. A standardized approach to these problems is required to optimize the outcome of surgery. This review aims to provide a simple yet comprehensive approach to dealing with the technical challenges encountered during revision knee arthroplasty.

Introduction

The ageing population and the increase in the number of previously performed total knee arthroplasties (TKAs) is resulting in an increasing burden of revision TKAs (RTKAs). Consequently, the modern-day knee arthroplasty surgeon must be equipped with the knowledge and skills to deal with the challenges posed by this ever-growing problem. When faced with a failing TKA, the most important initial step is to understand the underlying failure mechanism or mechanisms. One must then devise a clear plan to address the identified issues (which must include a Plan B, C and so on). Although it is important to have a standard and reproducible approach to managing a failed TKA, every revision scenario can pose unique challenges that may require an adaptable approach. In addition to the technical challenges of the surgery, other important points to consider include patient optimization, blood conservation strategies, postoperative medical support, dual consultant operating and holding a comprehensive implant inventory.

The current review aims to provide an evidence-based description of how to manage the common technical challenges encountered during RTKA. This will include a stepwise approach to include exposure, implant removal, joint reconstruction, implant fixation, management of bone loss, management of ligament insufficiency and, finally, soft tissue coverage.

Technical challenges

Exposure in revision TKA

Skin incision: the most common approach in primary and revision TKA is a midline skin incision combined with a medial parapatellar approach. It is recommended to perform a distal skin incision approximately 5–10 mm longer than the capsular incision, to ensure adequate distal closure of the capsule and to prevent distal capsular edge leakage. In a revision setting, it is important to note scars and approaches used in previous surgeries. In patients with multiple incisions from previous surgeries, it is recommended to use the most lateral scar, and, if possible, to consider preserving a skin interval of at least 6–7 cm. This is due to the fact that the blood supply to the skin in the anterior aspect of the knee is derived from blood vessels coming from the medial aspect. Small scars (<1.5 cm) can be safely ignored. Sharp scar angles (<60°) should be avoided due to the risk of compromising vascular supply of the flap. Finally, flap elevation should be performed as a single thick skin-subcutaneous layer below the superficial fascia.

Capsule incision and joint exposure: a medial parapatellar exposure remains the gold standard in primary and revision TKA. However, there are cases where a lateral parapatellar approach could be more advantageous. These cases include severe fixed valgus deformities with chronic lateral patellar subluxation and contracted lateral retinaculum, or pre-existing medialized tibial tubercle osteotomies with a narrow anteromedial window. The lateral approach is suitable when excessive lateral soft tissue releases and/or capsular Z-lengthening techniques on the lateral side of the knee are required. This will help maintain the vascular supply of the patella and prevent avascular necrosis.

In the vast majority of cases, careful and sequential dissection of the suprapatellar pouch and gutters will enable safe exposure of the joint. However, in some circumstances it may be necessary to employ ‘extensile exposures’. In addition, exposure will be easier if a hinged implant is being used, as resection of the collateral ligaments early on during joint exposure allows better access to the joint. The exposure in these cases includes a direct release of the medial collateral ligament (MCL) on the tibial and femoral sides. The tibia can then easily be dislocated anteromedially. The lateral ligaments are released from the femoral side to avoid injuring the peroneal nerve that runs posterolateral close to the tibiofibular joint. In cases of distal femoral replacement, a subperiosteal femoral release is performed around the condyles until the desired proximal level of resection is reached. The release sequence starts from the anterior and lateral aspects of the metaphysis, followed by the posterior release of the femur to enter the diaphysis. The knee is flexed, and a gentle posterior translation of the tibia will shift the neurovascular bundle posteriorly. Additionally, a thumb technique, pushing the popliteal soft tissues posteriorly, offers further control and protection of the vessels. For more proximal dissection, the femur will be elevated to provide the desirable soft tissue tensioning. Particular attention must be given to avoid any injuries to the extensor mechanism.

Extensile exposures: one of the most devastating complications in revision TKA is failure of the extensor mechanism (EM). Complex cases, with challenging exposure, are associated with a higher risk of disruption or avulsion of the EM. To allow adequate exposure of the joint while protecting the extensor mechanism from uncontrolled iatrogenic injuries that are difficult to reconstruct afterwards, reflecting techniques of the EM can offer an alternative to ease complex exposures by reconstructable detachment techniques of the EM. These can be performed on the distal portion via a tibial tubercle osteotomy or the proximal portion via a turndown V-to-Y-plasty and rectus snip technique. Other techniques described are the femoral peel or epicondylar osteotomy, which may require an additional screw fixation and/or a constrained implant to ensure joint stability.

A tibial tubercle osteotomy (TTO) is commonly performed for difficult exposures, preserving the periosteum with the attached anterior tibial muscle. ^, For managing severe patellar maltracking, a lateral to medial TTO can also be performed, combined with a lateral approach and a TTO medialization (if needed), without overstretching the lateral capsular structures. There are different dimensions of TTO described in the literature; however, in the revision setting, the most common osteotomy is 8–10 cm in length, 2 cm wide and 1.5 cm thick, to avoid iatrogenic fractures and to ensure a large bone contact area to optimize osseous healing and stability. For removal of well-fixed implants, a more extended TTO, adjusted to the length of stem, is required.

The quadriceps turndown is a modification of the V-Y technique that is based on a standard medial parapatellar approach, and extends via an inverted V incision across the quadriceps tendon and back down to the lateral retinaculum of the patella. This approach offers an intensive exposure of the proximal joint and a lengthening of the EM, with patellar distalization in cases of severe contractures of the EM (ankylosed knees), improving flexion. This can be performed by converting the inverse V incision to a Y. The literature suggests that this exposure is associated with poorer results due to extensor lag, and should be considered with caution. In addition, there is a risk of patellar devascularization as a result of injury to the superior lateral geniculate artery. Osteonecrosis of the patella can develop asymptomatically, and X-ray follow-up is recommended after this exposure. Extensor lag is another common complication, but this can be minimized by ensuring adequate rehabilitation.

The rectus snip technique is a modification of the turndown version, where the medial parapatellar approach runs oblique, laterally across the quadriceps tendon and the underlying rectus femoris tendon, preserving the lateral attachment of the vastus lateralis and the lateral blood supply of the patella. A lateral retinaculum release can be distally performed, protecting the superior lateral genicular vessels. The outcomes of this technique appear to be superior to the turndown technique, and should be used where possible instead of a formal turndown.

Implant removal

Polyethylene (PE) inserts are usually easy to remove utilizing an osteotome or a chisel. However, some implants have specific locking mechanisms that might require specific screwdrivers or other techniques. Surgeons must be aware of the implants that are in situ, and consult the respective manufacturer’s operative technique brochure for guidance, if needed. After PE removal, exposure to the joint may improve further. Explantation of the remaining components will make it easier to complete a posterior joint debridement. To unlock hinge implants with interlocking mechanisms, manufacturer-specific instruments are required. The implant removal starts from the femoral side, to ease a posterior approach to the tibial component. It is important to access the implant-cement interface to avoid unnecessary bone damage. Useful instruments that should be available in revision cases include rigid and flexible osteotomes of different sizes, a power saw with mini oscillating blade, a Gigli saw and a high-speed burr with different cutting tips. Finally, universal or implant-specific extractors, punches and hooks for retrograde explanation may sometimes also be required as well.

For cement removal, especially in the metaphyseal and diaphyseal medullary canal, high-speed drills, a burr, special cement osteotomes and hooks that are curved with offsets are commonly used. Finally, the use of an ultrasonic cement removal device has proven to be very useful, and is gaining popularity.

For modular implants with cones or sleeves, the epiphyseal components commonly dissociate, and can be removed to allow access to the metaphyseal bone-implant interface.

Removal of well-fixed implants in revision and re-revision cases can be very challenging, and is associated with an increased risk of complications. The implants to be wary of include the following:

(1)

well-fixed metaphyseal sleeves or cones
(2)

trabecular metal monobloc components
(3)

offset stems
(4)

long stems of large diameter (>14 mm) and increased surface roughness
(5)

curved stems
(6)

cylindrical cemented stems
(7)

deep cement plugs at the level of the diaphysis in the presence of an infection.

Compromised bone quality with thin cortical walls (e.g. after multiple revisions) can increase fracture risk. In these cases, an early osteotomy may save time and prevent further iatrogenic bone damage.

Osteotomies for the removal of femoral stems aim to preserve the blood supply of the periosteum. Stem extensions should bypass the osteotomy level and, where possible, cement extrusion between stem and osteotomy must be prevented, to reduce the risk of non-union at the site. Following tibial tubercle osteotomies, care must be taken to avoid anterior cortex fractures. Implant rotation can be established according to the tibial crest and the center of the ankle joint. Fixation of the TTO site can be carried out using either 4.5 mm bicortical screws (or 3.5 mm if cones/sleeves are used), cables or non-absorbable sutures. On the femoral side, cables are commonly used to fix osteotomies. In contrast to osteotomies for exposure, the osteotomies for implant removal are longer and based on stem length or the cement plug in the diaphysis that needs to be removed.

Basic principles of joint line reconstruction

The optimal reconstruction goal is to restore the native joint line of the knee and to correct possible alterations that may have been caused through previous failed arthroplasties. However, in most cases images of the ipsilateral or contralateral native joint are not available for use as a reference at the time of revision. Universal landmarks have been proposed to guide surgeons in reconstructing the joint line. These landmarks include 25–30 mm distal to the medial epicondyle; 20–25 cm distal to the lateral epicondyle, 20 mm proximal to tibial tuberosity, and 15 mm proximal to the fibular head. As a rule of thumb for intra-operative assessment, the joint line should be approximately ‘one finger’ bellow the distal pole of the patella (in cases where there is no patella baja), or more commonly ‘one finger’ above the fibular head. Where possible, placing the patellar button in a more proximal position, with excision of distal patellar osteophytes, may help avoid anterior impingement on the PE bearing. Pseudo-baja of the patella is mainly caused through elevation of the joint line during a TKA (iatrogenic), and should be corrected during a revision by distalizing the joint line to its native origin. About 35% of RTKA have a >5 mm elevated joint line. This is due to the bone loss, which frequently occurs at the distal femur, and is not addressed with distal femoral augments.

Joint line elevation >5–8 mm is commonly associated with inferior functional outcomes and problems such as anterior knee pain, anterior impingement of the patella, patellofemoral joint (PFJ) malfunction, increased collateral ligament stress, mid-flexion instability (especially in femoral components with a multi-radius sagittal profile), and an increased risk of stiffness. ^, Joint line distalization is associated with increased stress on the extensor mechanism, increased pressure on the PFJ, patellar subluxation, reduced flexion and mid-flexion instability.

Another important issue to address is restoration of the posterior condylar offset (PCO), as this can affect the outcome of revision TKA. Generally, an increase of >2 mm in the PCO is associated with a higher risk of flexion contracture, due to overstretching of the posterior structures and the posterior cruciate ligament (PCL) (with cruciate-retaining (CR) implant designs), mid-flexion instability (with single-radius femoral designs), and increased pain and stiffness that often require revision for offset correction. A decreased PCO, within 0–2 mm, may lead to reduced patellofemoral forces (particularly with mobile-bearing designs), and increased collateral ligament stresses, and in general, it is associated with inferior clinical outcomes compared to a neutral PCO or a 0–2 mm increased PCO.

Evidence supports that joint line and PCO restoration to its native pre-arthritic stage are important for successful outcomes and good range of motion after RTKA. However, about 40% of RTKAs show higher PCO values compared to their native reference. The accepted upper limit for PCO in RTKA is 4 mm. Although sagittal alignment is not associated with aseptic loosening in RTKA, it affects the anterior and posterior femoral offset, and care must be taken to prevent deviations above accepted boundaries. Cemented short stems are, for example, more prone to flexion of the femoral component than long press-fit stems that align to the femoral axis ( Figure 1 ). Finally, ligament instabilities should not be compensated with bony and implant positioning adjustments that may alter the joint line and PCO beyond the proposed limits. The reconstruction of the joint line in RTKA should begin from the tibia, as it affects both the extension and flexion gaps, and can be used as a reference for femoral rotation ^, It is preferable to reconstruct the tibial joint line with augments, and not by increasing the insert thickness. The drawbacks of a distalized tibial component are the risk of fracture due to impingement between stem offset adapter and the metaphyseal cortex of the tibia (depending on implant design and local anatomy), and the forced under-sizing of the tibial tray that may respectively limit the femoral size, which is important for the PCO reconstruction and flexion gap stability.