Osteoarthritis (OA) of the knee, known as gonarthrosis, causes significant movement
restrictions and pain in daily life activities. Total Knee Arthroplasty (TKA) is the
preferred treatment method for advanced-stage OA of the knee. While various alignment
techniques such as kinematic, constrained kinematic, and anatomical alignment are used,
the most commonly used and preferred method by researchers is TKA performed with a
technique that conforms to mechanical alignment.

Two main factors that affect patient outcomes after mechanically aligned TKA are
achieving a parallel joint line and appropriate positioning of the distal femoral
rotation that corresponds to the patellofemoral joint kinematics, ensuring optimal soft
tissue tension. If these two aspects are not adequately addressed, patients may
experience chronic pain, functional impairment, early wear at the implant interface, and
ultimately, loosening. Studies have reported that 8% to 19% of patients are dissatisfied
with TKA due to various reasons, including pain and unmet expectations. Problems that may
arise from malrotation and/or incorrect soft tissue tension include patellofemoral
instability, anterior knee pain, arthrofibrosis, and flexion gap instability.

In general, the natural joint line is not orthogonal to the tibial mechanical axis; it is
varus, ranging from 87 ± 3°. When the mechanical alignment technique is applied in TKA,
the proximal tibia and femur are typically cut perpendicular (90°) to the tibial and
femoral mechanical axes. However, in the case of symmetric implants, the classical
resection technique, especially in varus knees, results in more resection than the
component thickness in the medial femoral compartment and the lateral tibial compartment.
This creates an average 3° valgus joint line with respect to the tibial mechanical axis.
As a result, the joint line is preserved medially, but the lateral compartment becomes
more distalized.

Another issue regarding the joint line is its restoration, which involves achieving its
anatomical height. Changes in the joint line can lead to instability, increased incidence
of anterior knee pain, and decreased range of motion. The most commonly used bone markers
for the restoration of the joint line are the epicondyles, fibular head (FH), and tibial
tubercle (TT). Due to significant individual variations, some authors have suggested
using the ratio of the distance between the epicondyles and the tangent to the joint line
to the trans-epicondylar width (TEW) of the femur as a means of determining the
appropriate value. This ratio based on femoral width allows for the calculation of an
appropriate value for each individual regardless of size. However, it is not always easy
to radiographically identify the epicondyles, especially in varus knees with severe
metaphyseal damage.

On the femoral side, the width of the distal femoral resection should be equal to the
thickness of the metal implant to restore the normal femoral joint line level, regardless
of surgical techniques such as "measured resection technique" or modified "gap balancing
technique." During surgery, the distal surface of the medial femoral condyle usually
serves as the anatomical reference point for the distal femoral cut because in most
cases, thicker bone is cut and removed from the medial femoral condyle compared to the
lateral condyle. However, in patients with severely degenerated knees, significant bone
and cartilage defects occur in the distal femoral condyle, and the deformed medial
condyle is no longer a suitable reference point for distal femoral resection.

During total knee arthroplasty (TKA), bone defects are sometimes encountered. If there is
insufficient contact between the implant surface and the bone, augmentation is performed
on the bone defect to maintain implant stability. Researchers have investigated the use
of metal blocks in tibial bone defects during primary TKA and reported positive results,
emphasizing that the use of metal blocks is a simple and applicable method for tibial
bone defects.

In primary TKA, tibial or femoral defects, or both, are classified into three types by
the Anderson Orthopedic Research Institute: Type 1, small defects that do not compromise
component stability; Type 2, sponge-like bone loss requiring reconstruction, categorized
as A: involving one condyle or B: involving both condyles; Type 3, significant bone loss
jeopardizing a large portion of the condyle. Typically, in varus knee deformity, bone
defects in the knee appear first in the posteromedial region. In valgus gonarthrosis, the
tibial bone defect is central, while the femoral condyles have defects in the distal and
posterior lateral regions. Therefore, the primary classification of bone defects includes
distinguishing between central forms (defects confined within the peripheral bone cortex)
and peripheral forms (characterized by involvement of the peripheral cortex).
Additionally, in patients with varus alignment and gonarthrosis, differentiating between
intra-articular and metaphyseal sources of alignment defects is crucial as it can lead to
differences in postoperative clinical and radiological outcomes, requiring different
total knee arthroplasty procedures for patients.

Medial and lateral epicondylar axis (EA) has been used to determine the appropriate
location of the joint line (JL) during complex primary total knee arthroplasty (TKA) or
most revision TKAs. However, some studies have shown that selecting the epicondyles as a
reference can yield significantly different results. In these studies, the maximum errors
in intraoperative selection of the medial femoral epicondyle and lateral femoral
epicondyle were found to be 7.6 mm and 4.2 mm, respectively. Furthermore, the selection
of the medial epicondyle reported more varied results with errors up to 22.3 mm, while
the selection of the lateral epicondyle reported errors up to 13.8 mm. Additionally,
variations in the distance from the femoral epicondyle to the joint line can be up to 11
mm, and significant differences have been observed between male and female patients. In a
study conducted in the researcher's country, a correlation between the adductor tubercle
(AT) and the distance between the fibular head (FH) and the JL was investigated to
eliminate this handicap and determine the JL instead of using a mathematical ratio
between the epicondylar axis and the TEW. The study, conducted on a Turkish population
consisting of healthy volunteers, found the average TEW to be 87.2 ± 10.8 mm, the average
distance between AT and JL to be 47.9 ± 6.2 mm, and the average distance between FH and
JL to be 20.5 ± 4.0 mm. A strong positive correlation (0.55) was found between AT-JL and
TEW (adductor ratio - AR). Measurements related to AR calculation were performed on
radiographs of young patient knees without osteoarthritis. Based on this, another study
questioned the validity of AR by determining the differences between AR in knees with
severe osteoarthritis and those without osteoarthritis, considering the significant bone
and cartilage loss or osteophyte formation. In revision total knee arthroplasty cases,
intraoperative measurement of TEW and calculation of AT-JL may provide more accuracy in
determining the articular level compared to measurements taken on radiographs of knees
with severe osteoarthritis. They claimed that it could be more logical to measure TEW
intraoperatively instead of measuring it on primary or contralateral radiographs of
arthritic patients.

According to these two studies, the adductor tubercle can be used as a reliable marker to
determine the JL level in complex primary TKA or revision knee arthroplasty surgeries.
However, this new method has not been scientifically proven. In fact, there is no
generally accepted standard anatomical measurement system to accurately determine the JL
level on direct radiographs, especially in severely deformed knees with advanced varus.
There is also no consensus on the radiographic appearance to be used and the evaluation
of these images. A study found no significant difference (0.01 ± 0.03) between the
calculated AR (AT-EA/TEW) ratios obtained from radiographic and intraoperative
measurements. This method can be particularly beneficial in revision TKAs where the
anatomical EA is not clearly visible and provides a new tool for precise positioning of
prosthetic components and JL restoration even in such complex cases.

Literature lacks studies on determining the epicondylar axis using these methods for
advanced-stage gonarthrosis cases (Type M-F) characterized by severe bone-cartilage
defects, subchondral cysts, and extensive osteophytes in the medial femoral compartment,
which would render the determination of both the epicondylar axis and the AT location
impossible radiologically. Advanced imaging techniques such as computed tomography (CT)
or magnetic resonance imaging (MRI) can be used for these patients, but they are not
practically useful and add additional time and cost. Therefore, for patients with Type
M-F deformity who are candidates for total knee arthroplasty (TKA), a study will be
conducted to determine the JL location observationally without interfering with the
surgical technique, using both preoperative radiological measurements and intraoperative
caliper measurements. The measurements will be repeated in postoperative X-rays, and the
functional short-term outcomes will be evaluated over a period of two years.