What is the ACL?

The anterior cruciate ligament (ACL) is a band of tough tissue running from the tibia to the femur. The knee has two cruciate ligaments that cross each other (the other is the posterior cruciate ligament), hence the name ‘cruciate’. Its job is to provide stability to the knee. When the ACL is ruptured, it often results in increased motion of the femur on the tibia, particularly during movements that involve rapid direct changes or deceleration. This increased translation effect creates a sheering force on the articular cartilage, and the episodes of instability lead to abnormal motion of the bones that can result in damage of the meniscus and articular cartilage.

The ACL has the ability to form scar tissue, and on MRI can even look like it has healed back to its original form. However, MRI scans that are performed with the patient lying still and on their back are not good measurements of joint stability which is the primary problem created by an ACL rupture and often whilst the MRI looks healed on imaging, it has lost its function of providing joint stability.

Symptoms of ACL injury start off with acute swelling and  usually pain at the time of the injury. Often there is an audible ‘pop’ when it ruptures. After the joint swelling settles (weeks) the knee may feel quite good again, and may even return to feeling normal until it gives away again. Each instability episode may be damaging the cartilage and meniscus beyond being repairable, and functional instability is an indication for surgical intervention.

ACL injury

The ACL is typically injured during a sudden change of direction, twisting, jumping or landing that has gone wrong. It is often associated with a popping or loud noise, the sensation of the knee giving way followed by a rapid and large swelling which develops over subsequent hours or the next morning. Initially it is common patients are unable to weight bear and pain can often be severe early on.

Associated injuries

It is common to have associated injuries in addition to the ACL injury. The ACL is actually rarely injured in isolation. An associated injury includes tears to the meniscii which are the shock absorber of your knee, cartilage injury or additional ligament injuries. These associated injuries may alter management and time scales for surgery as well as  recovery.

The implications of ACL injury. 

When the ACL has been injured, activities and sports which involve twisting, pivoting, jumping and sudden changes in direction may become difficult and also may risk injuring the knee further. You may find that the knee gives way or that you have a lack of trust in your knee and therefore may find returning to these activities or even some activities of daily life difficult. Repeated giving way of the knee may lead to injury of the cartilage which is the smooth covering of the bones and possibly the meniscal as well. These secondary injuries are associated with a high risk of osteoarthritis of the knee later on in the patient's life.

Does a partial ACL injury exist?

Yes. Although this is a rare injury compared to  a full ligament rupture, partial ACL injuries may heal relatively well as there are still some fibres remaining intact which can act as a biological scaffold for the healing process. Treatment of partial tears will depend on the stability of the knee, the patient's aspirations, and other associated injuries. Patients with partial ACL injuries will need to be given a bespoke treatment pathway depending on their needs and goals.

Treatment Options for ACL Injuries

It is important to understand that not all ACL ligament injuries require surgery. After initial injury, pain and swelling will normally settle and it is usual that the patient can return to walking and straight line running with some simple rehabilitation.

Non-Surgical Treatment

ACL injuries can be managed non-surgically. Approximately 20-30% of patients who rupture their ACL may not require surgery. Usually these patients are over 30 years of age, participate in sports or activities that do not involve rapid decelerations or direction changes, do not have an associated meniscus or cartilage injury on imaging and do not have functional instability (episodes of the knee giving away). However evidence for determining which patients are appropriate for non-surgical management remains poor. Non-surgical management does carry the risk of having a non-repairable meniscus or cartilage injury and subsequent osteoarthritis and loss of knee function. A high-level study published in the Lancet in 2022 (The ACL SNNAP Trial) showed that in appropriately selected patients, knee function and symptoms was significantly better after 1 year comparing surgical reconstruction to non-surgical treatment of ACL injury. The study followed patients for two years and showed, with time, this difference became even greater. The financial cost over the two-year period was also more when patients were treated non-surgically.

Bracing

Recently there has been renewed interest in managing ACL injuries by bracing the knee in flexion for a period of approximately 6 weeks (‘cross-bracing’ method). Whilst evidence for this treatment option is still emerging, early data suggests that partial or ‘lower grade’ type ACL injuries may be suitable for this treatment modality and may be treated successfully non-surgically. Higher-grade ACL injuries or those with associated injuries however appear to have a high failure rate with this treatment modality (over 20% at 1 year).

Surgery

Surgery is preferred in high grade ACL ruptures such as those with high energy injury patterns ie certain meniscal tears, significant bone bruising or sub-chondral fractures,  a high degree of clinical instability, additional ligament injuries, people wishing to participate in high level pivoting sports or those who have failed non-surgical treatment.  Surgical reconstruction involves using a piece of tissue either taken from the patient (autograft), synthetic or a person who has donated their tissue (allograft) to create a new ligament. This is passed into two tunnels, one in the tibia and one in the femur. Any meniscal and cartilage pathology may also be addressed at the time of the surgery. This is then fixed with any combination of screws, buttons, anchors, or sutures. 

In some circumstances, additional ligaments may have been injured when the ACL was torn such as the medial collateral ligament (MCL). This may, as part of your ACL surgery, require repair or reconstruction. For example, MCL injuries do scar and may looked ‘healed’ on MRI imaging, however in some cases they remain stretched, have residual laxity (looseness) compared to the other knee and do not return to their original state. Residual laxity after MCL injuries has been shown to increase the risk of re-injuring the ACL graft. MCL surgery involves making an incision on the inside of the knee and suturing the torn or stretched tissues. A graft may be required to reinforce the repair and this can be either from a donor (allograft), the patients tissue (autograft) or synthetic (material). It is held in place with either sutures, anchors or staples or a combination.

Surgical management

A number of graft choices exist. The most popular graft choices are hamstring tendons, followed by part of the patella tendon with some bone or part of the quadriceps tendon. Each graft has its own specific risks, advantages, and disadvantages. Graft choice may vary from patient to patient and should be tailored to the individual patient. This forms part of the discussion during consultation.

Surgical management is typically advised for patients who are experiencing functional instability although they wish to return to at risk sports and activities that involve pivoting maneuvers. Certain associated injuries may also demand surgical reconstruction.

The primary aim of surgery and the post-operative rehabilitation is to stop the knee from giving way and to improve its overall stability. These aims include;

1. To allow individuals to return to the normal activities of daily living and sport

2. To increase the confidence the individual has in the knee

3. To be "chondroprotective" i.e. to protect against secondary injury to the meniscal and cartilage

It is important to understand that good surgery with the appropriate does not result in a normal knee. However, published research shows that approximately  90% of individuals considered their knee to be functioning normally or nearly normally following surgery. Return to sport can be more variable and is influenced by a number of factors including the time from injury to surgery, fear of reinjury, personal and work-related factors, as well as associated injuries.

It must be emphasised, that reconstructing the ligament alone does not guarantee success. Surgery without the appropriate post-operative rehabilitation can result in a high risk of re-rupture, ongoing instability, and anterior knee pain. You are expected to follow an exercise program that is guided by a suitably trained physiotherapist for up to a year depending on your overall goals.

ACL reconstruction

Graft choices

A number of graft choices exist. The most popular graft choices are hamstring tendons, followed by part of the patella tendon with some bone or part of the quadriceps tendon. Each graft has its own specific risks, advantages and disadvantages. Graft choice may vary from patient to patient and should be tailored to the individual patient. This forms part of the discussion during consultation. 

1. Hamstring tendons. These 2 tendons are usually taken through a small incision on the front, inner aspect of the tibia or shin bone. Variations exist in terms of taking either 1 or 2 of the hamstring tendons named semitendinosus and or Gracillis. 

2. Patella tendon or also known as bone patellar tendon bone graft. The patellar tendon graft is made from a central strip of the patellar tendon that runs from the kneecap or patella down to the tibia or the shin bone. A central strip of tendon is harvested with a bone block at either end taken from the patient. This involves a larger incision over the front of the patient's knee.

3. Quadriceps tendon. This graft is taken from a small incision above the knee and is made from a central strip of the quadriceps tendon which is the tendon that attaches your quadriceps or thigh muscles to your knee cap.

4. Allograft. This is a donor graft taken from another person. It is treated chemically or sometimes by irradiation. It is used in specific circumstances and is not suitable for all patients. 

5. Synthetic material. Synthetic material is available, and previously has been used to perform ACL reconstruction. However, due to some serious and unfortunately frequent complications associated with the use of synthetic ACL reconstruction, this is rarely used nowadays. Synthetics may be used for ligament reconstruction is that are not required in the knee joint but are no longer typically used in ACL surgery.

Your surgeon may discuss graft choices with you and the choice will depend on a number of factors including your examination, the sports you wish to participate in, your age, your own personal desires and requirements, as well as the known risks and benefits of each of the above graft options.

Graft fixation

The new graft is inserted into the knee through a tunnel in the tibia and also through a tunnel in the femur. It is secured into both of these tunnels via one of several methods. This typically is either done with the use of a screw or another fixation device such as a metallic button or staple and rarely needs to be removed.

Meniscus surgery

The meniscii are commonly injured with an ACL rupture and it is not uncommon for patients to require either a meniscal repair or partial meniscal resection during the ACL reconstruction. This may alter the post-operative rehabilitation and your surgeon will speak to you about this either prior to or after the surgery. 

Lateral extra-articular procedures or LEAP’s

Some patients are offered an additional procedure termed a LEAP. This can either be as a procedure called a lateral tenodesis or an anterolateral ligament reconstruction. This involves an incision on the outside of your leg, typically on the outside of your knee to harvest a small strip of tissue from a structure cord the iliotibial band or ITB. This tissue is then used to reinforce the knee and is attached to your femur by one of a number of ways. This can be done by way of an anchor, screw or stable. It aims to provide additional stability to the knee and has been shown to reduce the risk of re-rupture. It is common for patients to have some increased pain and swelling after ACL surgery if they had a lateral tenodesis in the early post-operative phase. The knee may also feel slightly tighter. The surgeon will assess your individual factors to determine if a LEAP procedure is appropriate.

Potential Risks and Complications of Surgery

Fortunately, serious complications are rare. However, it is important that you look after your knee, and if possible, identify any problems early so they can be treated quickly.

The risks of ACL reconstruction are:

General

• Being made worse

• Failure to return to desired level

• Risk of deep infection (requiring multiple returns to theatre for arthroscopic lavage, long-term antibiotics and possible revision of the surgery)

• Superficial wound infection

• Further surgery

• Progression of the osteoarthritis

• Persistent swelling (synovitis)

• Neurovascular injury (numbness around scars and injury to the major nerves and vessels supplying the lower leg that leads to potentially permanent muscle weakness)

• Haematoma and bruising

• DVT

• Pulmonary embolus

Specific

• Re-tearing or failure of the ACL graft and need for revision surgery

• Meniscal repair or meniscectomy

• Chondroplasty and microfracture

• Restriction on weight-bearing and movement post-surgery

• Restrictions on flying, driving and participating in sport

• Difficulty interpreting MRI findings post operatively (repair lines and scar tissue often confused for ‘tears’)

• Multiple scars (size and number depend on associated injuries and surgery)

Specific Risks to Graft Choices

Hamstrings

• Hamstring pain

• Clicking over the pes anserinus region

• Numbness

• Posterior thigh pain with sprinting

• Need to harvest alternate graft (contralateral hamstrings, quadriceps tendon or bone-patella-bone)

Bone-Patella-Bone

• Anterior knee pain

• Difficulty and discomfort kneeling

• Large anterior scar and subsequent numbness

• Post operative recovery may include more pain and possibly be more difficult

• Patella fracture 

• Patella tendinopathy

• The risk of osteoarthritis may be slightly higher than other graft choices

• Need to convert to alternative graft choice

Preparing for surgery

Preoperative preparation

You will be advised on the appropriate preoperative rehabilitation to get the knee ready for surgery. This will include physiotherapy that is aimed at achieving a good range of motion. The precise amount and type of physiotherapy is to be determined by the therapist. This is defined as being able to achieve near full extension, being able to flex the knee past 90 degrees and to reduce the amount of swelling that is in the knee. It is also critical to be able to activate and to maintain the strength of your quadriceps, hamstring and gluteal muscles prior to the surgery. Recent literature on this topic has shown that this helps optimise your recovery from ACL surgery and may even help prevent certain complications. Specifically, it is critical to avoid a condition that has recently been termed ‘arthrogenic muscle inhibition’. Failure to achieve an adequate range of motion or activation of the muscles prior to surgery may result in the surgery being postponed or even cancelled.

During the pre-surgery period you will also be encouraged to walk normally and to even eventually do away with crutches once your quadriceps control has been regained. It is often helpful in this phase to have a compressive bandage on the knee such as a Tubigrip or else other prescribed by your physician. Certain devices that are referred to as ice compressive sleeves may also be particularly helpful in terms of reducing pain and helping reduce swelling in both the pre- and post-surgical period. Unfortunately, these devices need to be hired and have an associated additional cost. However, if it is within the patient's financial ability, the use of such devices in order to assist with the above goals is strongly recommended. More information on these devices can be obtained by speaking to our administrative staff.

Muscle strength and conditioning

There is evidence to demonstrate that patients who improve their quadriceps strength and mobility prior to knee surgery make both a faster recovery and tend to recover greater function following the surgery. It is recommended that you undertake a strength and conditioning program supervised by a qualified health professional such as a physiotherapist.

Supplements

Prior to surgery, it is critical that you maintain good health. As part of this some supplements have been shown to be beneficial. These include iron supplementation to boost haemoglobin levels if they are low, vitamin D to improve your immune system and bone health. In addition to this, patients should ensure that they have a healthy diet that avoids excessive consumption of alcohol. For patients with diabetes, good blood glucose control is critical for reducing the risk of post-surgery complications, such as infection and wound breakdown.

Iron supplementation may not be recommended in some individuals with certain medical conditions. Advice should be sought from your medical practitioner before commencing this medication.

Recent evidence has emerged showing the use of branched chain amino acid supplements enhances muscle recovery following knee surgery. Whilst this was a small study, it was a randomised controlled trial comparing to a placebo supplement and demonstrated less fatty striations in the leg muscles of patients taken the supplement. Branch chain amino acid supplements are not suitable in patients with kidney disease or poorly controlled diabetes. They can be purchased if the patient wishes to use them as adjunct in their recovery.

Pre-existing medical conditions

You will be asked about your medical history. It is important that you accurately inform your specialist of any conditions affecting your heart, lungs, blood pressure, kidneys, or circulation. It is also critical to inform your doctor of any conditions that may affect your immune system such as diabetes. 

Medications

10 days prior to surgery some medications may need to stop. These may include aspirin, nonsteroidal anti-inflammatories, garlic capsules and fish oil. If you are taking blood thinners such as aspirin, Plavix, or warfarin these may need to stop but will likely need to be done in conjunction with the advice from either your general practitioner or another specialist such as a cardiologist. It is critical that you inform your specialist if you are taking these medications.

Skin care

It is vitally important that you have no cuts, scratches, or skin infections as these increase the risk of infection and may lead to your surgery been postponed. Do not wax or shave your legs in the week prior to surgery.

Smoking

It is recommended to cease smoking for at least 6 weeks prior to surgery. People who smoke have an increased complication rate for events such as a DVT, infection, or wound complications.

The day of the surgery

Bring all x-rays and scans with you to the hospital. You are usually admitted to the hospital of surgery where you will meet the anaesthetist who will discuss your medical and anaesthetic history. The anaesthetist will also discuss the type of anaesthetic being used during your procedure, which is most commonly a general anaesthetic. You will be giving fasting instructions. It is critical you adhere to the fasting instructions. Deviation from any instructions may result in cancellation of surgery.

On admission, your leg is washed, shaved, if necessary, prepared with antiseptic and wrapped in a sterile towel. This helps prevent infection and helps identify the correct site for surgery. Prior to the surgery you will be repeatedly asked to confirm which side will be operated on. These are important checks for the hospital staff to perform.

The surgery

The operation takes between 60 and 90 minutes and is largely performed arthroscopically or by keyhole surgery. In general, the ACL is replaced with a graft taken from the patient's own tissue. This brief procedure is performed usually as day surgery and typically the patient will go home on the same day. Variations from this may exist depending on additional procedures, the anesthetic given and the patient's individual factors.

Intravenous antibiotics are given at the start of surgery. Surgery is performed with a tourniquet around the leg. Depending on the graft choice, an incision will be made at different locations to harvest tissue. For example, a hamstring graft is harvest via small 3cm incision on the inner aspect of the shin just below the knee. An arthroscopy is then performed to inspect the joint cartilage surfaces, remove any loose bodies and treat any associated meniscal injuries if required.

Once the graft is prepared and any meniscal surgery undertaken, tunnels will be created by drilling into the femur and tibia bones and the graft then passed and fixed. Typically, the graft is fixed using a combination of sutures attached to some small metallic buttons. In some instances, a lateral extra articular procedure will performed (see information on this). Dr Shatrov will discuss this with you if this is to be performed.

At the conclusion of the procedure, local anaesthetic is infiltrated into the wound to reduce post-operative pain. Dressings are applied and a brace placed on the leg.

After Surgery

After surgery you will have padding and dressings covering your knee. Pain following the surgery will vary considerably between individuals, but you are likely to have some soreness around the knee and graft harvest site. It is very important to control the knee swelling by resting and elevating the leg as much as possible, especially in the first 48 to 72 hours. For this, we strongly advise the use of ice compressive sleeves. Additional information about this can be obtained by speaking to our administrative staff. You should apply the ice regularly wrapped in a damp towel for no longer than 20 minutes at a time in order to avoid ice burns and this should be repeated every 2 hours in the first 4 days.

Weight-Bearing

After surgery, weight-bearing will be determined by any meniscal and cartilage injury or associated ligament surgery. If weight-bearing is permitted, crutches are still required until the quadriceps have regained control of the knee and walking can be performed safely. Patients typically go home the same day of surgery. 

Bandages and Dressings

On the first after surgery, the bandages on the knee are removed and a compressive bandage called a tubigrip, which has been placed underneath from mid shin to mid-thigh, is left in place. The dressings are kept dry and in place until the wound review, which is performed with the surgeon typically 10 to 14 days after the surgery. If the bandaging becomes soaked either with blood or otherwise the patient should return either to the clinic, or if this is not possible, to the hospital to have the dressings changed.

Stitches in the incisions may be dissolving, however are still removed between days 10-14 on a return visit to consultation for a wound review. The knee needs to remain dry. Swimming, bathing, spa’s, sauna etc. is not allowed until wound healing is confirmed. In order to shower, a water-proof sleeve that fits over the knee can be purchased from the chemist.

Exercises

Exercises to activate the quadriceps and gluteal muscle are performed, and calf pumping exercises encouraged to circulate blood throughout the leg. The focus initially should be on achieving full extension of the knee and activating the quadriceps muscles. Flexion of the knee is typically encouraged as well but may be limited depending on some of the associated injuries or surgery that your knee may have required such as meniscal surgery.

Medications

A blood thinning medication is often prescribed for two weeks following surgery to reduce the risk of DVT’s. 

Pain relief is prescribed and typically involves the following; 

Paracetamol 1 g every 6 hours (if the patient does not have either an allergy to this medication or pre-existing liver disease) 

A nonsteroidal anti-inflammatory which is typically either 1 of celecoxib, meloxicam or Voltaren. This should not be taken if the patient has kidney problems, high blood pressure, may be pregnant or has reflux. 

Additional pain killers are often prescribed but depend on a variety of factors including the anaesthetist’s preference, the patient's preference, and pre-existing medical conditions as well as their medication history. Local anaesthetic is typically injected around the incisions and graft harvest site at the time of surgery and often wears off 12 to 18 hours after being inserted. This is often accompanied with gradually increasing pain at that time. If ongoing scripts for analgesia are required, these should be sort from your GP.

Driving 

Driving is not permitted until sufficient muscle control has been regained to allow for emergency breaking. The length of time that this takes varies depending on the surgery and can range from 1 week to 3 months. Driving is also not needed whilst taking certain medications. For more information about this please consult either your general practitioner or your orthopaedic surgeon.

Showering

Showering is permitted but the wound needs to remain dry. A sleeve can be purchased from some chemists. Alternatively, a bag can be wrapped around the leg to keep it dry.

Bracing

Bracing is not performed routinely however may be required when ACL surgery is performed in conjunction with other associated injuries such as meniscal repair or additional ligament surgery.

Physiotherapy

A critical component of ACL recovery is a supervised rehabilitation program with a physiotherapist. Physiotherapy should be arranged prior to surgery and the details of the physiotherapist shared with the surgeon so they can communicate as required during your recovery.

Rehabilitation

Rehabilitation following ACL reconstruction is a 9 to 12-month programme broken into 4 main stages which will overlap. You will be guided through these phases by a physiotherapist.

1. Recovery from surgery; swelling management, early range of motion and basic movement re-training including gait and re-education.

2. Progressive limb loading, basic strength training and neuromuscular control involving balance and movement control. Early regain of cardiovascular fitness.

3. Return to running and jump land control. Focusing on preparation for returning to running and sport. This involves a higher level of rehabilitation.

4. Athletic enhancement and return to sport. To ensure you are ready to return to sport you will need to pass our return to sport testing protocol which is typically performed around the 9-month mark. This includes an MRI assessment as well as strength and movement analysis and other tests and questionnaires that have been validated and used for patient's recovery after ACL surgery. 

Physiotherapy

Depending on where you have had your surgery performed and whether you are a public or private patient, you may choose to have your physiotherapy through a private clinic with a physiotherapist of your choosing, or through a public hospital outpatient physiotherapy clinic. Whilst the decision of the physiotherapist is ultimately up to the patient you may wish to discuss therapist choice or options with your surgeon. Ultimately it is critical that both the patient and surgeon have an excellent enclosed working relationship with the physiotherapist.

It is strongly advised that physiotherapy is commenced prior to the surgery and is also started within the first week following the surgery. The frequency and exact length of physiotherapy sessions should be determined by the therapist and will vary based on various patient, injury and surgical factors.

Orthopaedic follow-up appointments

You will be reviewed typically at the following time points; 2 weeks for a wound review, 6 weeks, 3 months, 6 months and then finally 9 or 12 months after the surgery. Variations to this protocol may vary based on your recovery as well as variations to the surgery that was performed

Dr Shatrovs Publications on ACL Injuries

1. Shatrov J, Freychet B, Hopper GP, Coulin B, El Helou A, An JS, Vieira TD, Sonnery-Cottet B. Radiographic Incidence of Knee Osteoarthritis After Isolated ACL Reconstruction Versus Combined ACL and ALL Reconstruction: A Prospective Matched Study From the SANTI Study Group. Am J Sports Med. 2023 May 8:3635465231168899. doi: 10.1177/03635465231168899. Epub ahead of print. PMID: 37154412.

2. El Helou A, Gousopoulos L, Shatrov J, Hopper GP, Philippe C, Ayata M, Thaunat M, Fayard JM, Freychet B, Vieira TD, Sonnery-Cottet B. Failure Rates of Repaired Bucket-Handle Tears of the Medial Meniscus Concomitant With Anterior Cruciate Ligament Reconstruction: A Cohort Study of 253 Patients From the SANTI Study Group With a Mean Follow-up of 94 Months. Am J Sports Med. 2023 Mar;51(3):585-595. doi: 10.1177/03635465221148497. Epub 2023 Feb 3. PMID: 36734511.

3. Mesnard G, Fournier G, Joseph L, Shatrov JG, Lustig S, Servien E. Does meniscal repair impact muscle strength following ACL reconstruction? SICOT J. 2022;8:16. doi: 10.1051/sicotj/2022016. Epub 2022 May 16. PMID: 35579438; PMCID: PMC9112909.

4. Cance N, Erard J, Shatrov J, Fournier G, Gunst S, Martin GL, Lustig S, Servien E. Delaying anterior cruciate ligament reconstruction increases the rate and severity of medial chondral injuries. Bone Joint J. 2023 Sep 1;105-B(9):953-960. doi: 10.1302/0301-620X.105B9.BJJ-2022-1437.R1. PMID: 37652445.

5. Foissey C, Batailler C, Shatrov J, Servien E, Lustig S. Is combined robotically assisted unicompartmental knee arthroplasty and anterior cruciate ligament reconstruction a good solution for the young arthritic knee? Int Orthop. 2022 Aug 13. doi: 10.1007/s00264-022-05544-5. Epub ahead of print. PMID: 35962232

6. Shatrov J, Bonacic Bartolin P, Holthof SR, Ball S, Williams A, Amis AA. A Comparative Biomechanical Study of Alternative Medial Collateral Ligament Reconstruction Techniques. Am J Sports Med. 2024 May;52(6):1505-1513. doi: 10.1177/03635465241235858. Epub 2024 Mar 29. PMID: 38551132; PMCID: PMC11064462.

7. Shatrov J, Jones M, Ball S, Williams A. Factors affecting return to sport in elite athletes after microfracture for chondral lesions in the knee. Orthop Procs. 2023;105-B(SUPP_13):73-73. doi:10.1302/1358-992X.2023.13.073