Reviewed by – Dr. Satish Reddy
Many considering an ACL surgery have questions on what type of screws, biodegradable screws or metallic screws, would give the best outcome. There are many factors to be considered before choosing one. Let’s see the details about choosing the biodegradable screws or metallic screws for ACL Surgery.
What is a Cruciate Ligament?
Cruciate ligaments are present within a knee joint. They are a pair of ligaments which cross each other to form an ‘X’ and are therefore known as cruciform or cruciate ligaments. These ligaments stabilize the knee during its back and forth movements.
Anterior cruciate ligament (ACL) is located diagonally in front of the posterior cruciate ligament, in the middle of a knee. ACL is attached to the thigh bone (femur) and shin bone (tibia). It controls rotational movements of a knee and prevents the shin bone from sliding above the thigh bone during knee flexion.
What is an ACL injury?
Anterior cruciate ligament injury may result in pain, swelling, diminished range of motion, and discomfort in the knee.
ACL may either get sprained or may undergo a partial or a complete tear. An injury to this ligament can be caused due to:
- A sudden change in direction of the knee.
- A sudden halt while walking or running.
- An incorrect landing from a jump.
- A forceful impact on the knee.
An ACL injury is one of the most common knee injuries. It is most prevalent among athletes, sports-person, and physically active individuals.
When would you need an ACL surgery?
Most of the anterior cruciate ligament tears are complete, that is, a partial tear of an ACL is less common. An ACL tear usually requires surgical repair, unless stability of the knee hasn’t been compromised and if the patient has a sedentary lifestyle. Sometimes, non-surgical treatment of an ACL tear may be considered, for instance in elderly patients.
ACL sprains generally do not require surgical correction. However, if you have a torn ACL with knee instability, surgical intervention is the only treatment.
Most ACL tears cannot be stitched or sutured, and need a surgical intervention.
What is an ACL surgery?
An ACL reconstruction surgery involves replacement of anterior cruciate ligament by a tissue graft. A new ligament grows on the tissue graft approximately six months after the procedure.
Tissue grafts can be obtained from patient’s own body (autograft), such as from patellar tendon or hamstrings tendon; or from other sources (allograft).
During the surgery, a tissue graft is secured by interference screws which help in securing the tendon into bones (tibia and femur).
Initially, titanium was the material of choice for interference screws, used in ACL reconstruction surgeries owing to its biocompatibility. Lately, biodegradable screws are widely used.
A bioabsorbable or biodegradable screw automatically resorbs or disintegrates in our body, unlike a metallic (titanium) screw.
An anterior cruciate ligament reconstruction surgery is minimally invasive and requires small incisions. Post-surgical rehabilitation is an important determinant to a successful recovery.1
Who decides the type of graft and screw to be used in an ACL reconstruction?
Usually, a surgeon decides on the type of tissue graft to be used, but you will be asked to choose between biodegradable or metallic screws, prior to surgery. The total cost of surgery varies with the type of screw chosen since biodegradable screws cost higher than their titanium counterparts.
An ACL reconstruction surgery costs between 75,000 and 1.5 lac rupees in India. Sometimes, patients also choose metallic screws in the case of a budget constraint.
So what should you choose?
Recently, biodegradable interference screws have been widely used in ACL reconstructions. Apart from being more expensive, biodegradable implants have other major drawbacks such as foreign body reaction, incomplete bone formation (after implant/screw resorption), and a slower rate of graft tissue formation.
Titanium screws though biocompatible may result in an increased risk for infection if retained; hence a second surgery is required for removal of the screw. Additionally, these implants interfere with diagnostic imaging; make revision surgery difficult; and may induce stresses in the surrounding bone causing a reduction in bone density.
Now the question is, which of these interference screws will provide you with better long-term results?
In 2014, British Medical Bulletin reviewed the outcomes of different materials for fixation screws in ACL reconstruction. It was observed that both biodegradable screws and metallic screws had similar results with regard to the clinical scores, evaluation, and imaging assessment of patients. Biodegradable screws were considered superior due to their property of osteointegration (integration with the surrounding bone). However, higher costs of these screws could not be justified, since the long-term results of metallic screws were equivalent.2
In 2015, The Journal of Arthroscopic and Related Surgery published a study which showed that biodegradable screws caused prolonged fluid accumulation around the joint (fluid effusion), increased femoral tunnel widening (widening of the bone surrounding the screw), and screw breakage. Here, functional comparisons between the two types of screws did not show significant differences.3
Another interesting study in 2015 conducted a 5-year follow-up post-surgery, comparing metallic screws to PLLA-HA (L-lactic acid with hydroxyapatite) screws – a type of biodegradable screw. It was shown that unlike metallic screws, PLLA-HA screws were not associated with femoral tunnel widening or increased cyst formation. Although these screws showed incomplete ossification of the surrounding bone after screw resorption, no adverse effects were noted over 5 years.4
A recent study in 2016, searched medical databases to compare the functional outcomes of ACL surgeries with bio-degradable screws and metallic screws, in 944 patients. Patients from both groups (with biodegradable screws and metallic screws) reported similar knee functions, one, two and five or more years post-surgery. Furthermore, the levels of activity of patients with either screw type did not show any differences.
However, biodegradable screws were associated with more treatment failures, like screw breakage during placement and graft rupture.5
So let us summarize the advantages and disadvantages of biodegradable screws and metallic screws used in ACL reconstruction surgeries.
Advantages 6, 7
|Biodegradable Screws||Titanium Screws|
|MRI imaging is possible post-surgery.||No foreign-body reaction.|
|No long-term interference with surrounding tissues.||No tunnel widening of the surrounding bone.|
|The need for a second operation for screw removal is eradicated.||Faster biological tissue (new ligament) regeneration.|
|Reduced risk of infection.||Easier placement.|
|No osteoporosis (brittle bone disease) or stress in tissues surrounding the screw.||No fluid effusion.|
|No osteolysis (bone depletion) or cyst formation.|
Disadvantages 8, 9
|Biodegradable Screws||Titanium Screws|
|Do not necessarily resorb at defined rates – i.e., they vary in their rates of degradation.||Do not resorb over time – causing distortion of diagnostic images and making visualization of surrounding tissues difficult.|
|Slower rates of biological tissue (new ligament) regeneration.||MRI imaging cannot be done post-surgery.|
|May cause inflammatory or foreign body reactions leading to osteolysis or cyst formation.||Interfere with revision surgeries as they are difficult to remove.|
|Require precise technique due to inadequate stiffness and a higher rate of breakage.||Second surgery is required for screw removal.|
|May result in incomplete ossification (bone formation) and tunnel widening in the surrounding bone.||May cause metal sensitivity or localized irritation and pose a risk of infection if retained.|
|Have rapid loss of implant (screw) strength leading to higher fracture rates.||Cause stress shielding or reduction in bone density in the surrounding area.|
|Cause fluid-effusion – collection of fluid around the joint.|
Do you need a specialist?
An ACL reconstruction surgery is a technique sensitive procedure, hence it will be performed by an experienced orthopedic surgeon. If you are choosing to go for a biodegradable screw, you must find out whether the surgeon performs such procedures often.
Biodegradable screws require more precision during placement. If your surgeon has experience in similar surgeries, chances of the procedure being a success, increases.
You could ask your physician or family members if they know of an experienced orthopedic surgeon. Patient reviews may also help to a certain extent, in this aspect.
Since most of the medical research findings suggest that long-term outcomes of both biodegradable screws and metallic screws are similar and satisfactory, main criteria for selection depend on the patient’s age and budget.
If you are young, you may require a revision surgery at a later stage, hence the best option for you would be to choose a biodegradable screw.
Whereas, if your doctor does not anticipate a need for a revision surgery in your case or if your activity aspirations after recovery are limited and you have a limited budget, a metallic screw would be a good choice for an ACL reconstruction surgery.
Ultimately, it is important to know that although a biodegradable screw costs more, its superiority over metallic screws with respect to outcome and function has not been proven on long-term analysis. Your orthopedic surgeon can be your best guide in deciding on the type of interference screw best suited for your joint, based on your medical condition and the pros and cons of ACL reconstructions with biodegradable screws and metallic screws.
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