Over recent years, there has been a noticeable increase in capsular ligament lesions of the knee joint (about 60-80 per 100,000 members of the population according to one Swiss accident statistic). In 65% of cases, these knee injuries have been caused by sports accidents, primarily by skiing, followed by football, baseball, American football and basketball. Amongst ligament injuries, anterior cruciate ligament (ACL) injuries rank top with 47.6%, followed by isolated medial collateral ligament (MCL) injuries and ACL tears combined with MCL tears.
Most ACL injuries that we see are the result of a non-contact twisting movement, usually due to abrupt deceleration and change of direction. Patients generally describe a feeling of instability and most of them hear or feel a crack when the injury occurs. After the injury, patients are generally unable to continue with their sport, frequently followed by immediate severe swelling of the knee joint (swelling due to meniscal lesion or arthrosis overstrain takes 1-2 days).
Problems associated with cruciate ligament tears
The anterior cruciate ligament (ACL) stabilizes the lower leg (shinbone) against dislocation to the front, while the posterior cruciate ligament (PCL) provides stability to the rear. Absence (tear) of the cruciate ligament causes instability (loose knee joint).
Even in normal walking, this instability results in abnormal displacement, which can cause the knee to "give way", particularly under the stress of sporting activities.
This causes damage to other important structures of the knee joint, such as the meniscus, collateral ligaments and cartilage surfaces, resulting in a lowered exercise tolerance and increased arthrosis even in younger people.
For this reason, it is generally advisable to replace the anterior cruciate ligament. Suturing or replacing the ACL with an artificial ligament is internationally not considered to be a promising option.
Selection and fixation of the transplant
Several graft options are available for ACL replacement; common to all is their greater tear resistance.
Tear resistance of the normal cruciate ligament and different grafts
| Normal ACL Ligamentum patellae (10 mm) Quadruple hamstring Quadriceps tendon (10 mm) |
2160 to 2317 Newton 2376 to 2527 Newton 4108 to 4308 Newton 2352 to 2837 Newton |
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Ligamentum patellae (patellar tendon)
The patellar tendon is about 25 mm wide. A 10-11 mm strip of it together with a bone plug at each end from the patella and the top of the tibial head can be taken. The primary tear resistance of an 11 mm patellar tendon graft is about 40% higher than that of the normal human ACL.
The advantages of this graft are its high initial tear resistance, the good fixation of bone to bone with excellent primary stability and stiffness as well as osseous integration.
Its disadvantages are pain at the site from where the graft has been taken, a possible reduction in the muscular strength of the quadriceps muscle as well as the possible (though actually rather rare!) risk of a patellar tendon tear or a patella fracture. Statistically, anterior knee pain is more common in the first year after arthroscopic replacement of the ACL with a patellar tendon graft than after replacement with a quadruple-hamstring graft.
Patellar tendon graft with
2 bone plugs
Quadriceps tendon (tendon of the thigh extensor)
The quadriceps tendon is about 35 mm wide. As with the patellar tendon with a bone plug, a 10-11 mm strip can be taken from the patella. The primary tear resistance of an 11 mm quadriceps tendon graft is comparable to the tear resistance of a patellar tendon graft.
Quadruple hamstring graft (popliteal ligaments: semitendinosus tendon and gracilis tendon)
These tendons are taken from the interior tibial head through a small incision in the skin and then folded over to result in a four-layer (quadruple) graft. The primary tear resistance of a quadruple hamstring graft is about twice as high as that of a normal human ACL.
The advantages of semitendinosus and gracilis grafts are lower complication rates, less pain after harvesting the tendons and only a small, cosmetically inconspicuous scar.
In addition, this type of graft is more likely to match the stiffness of a normal ACL. Restrictions in movement have been proven to be comparatively rare. The maximum tear resistance of a quadruple hamstring graft is even higher than that of the patellar tendon.
It is seen as a disadvantage that the integration of the tendons into the bone channels takes longer compared with the integration of the patellar tendon. The bone plugs of the patellar tendon integrate with the bone within 3-6 weeks, while the popliteal tendons require 10-12 weeks.
Quadruple hamstring graft
(4-fold popliteal tendon)
Donor tendon (allograft)
A donor graft (allograft) has the advantage of unlimited graft size plus the fact that no tendon has to be taken from the patient. There is no additional weakening of the knee joint, while for the patient the operation itself constitutes only minimal stress and a small dermal scar. As a rule, these allografts are human Achilles or patellar tendons, which we receive from Eurotransplant in the Netherlands. They are prepared according to the latest scientific insights. The results of donor grafts are as successful as those of the other grafts described earlier. Any risk of infection from hepatitis or AIDS has been practically excluded, because the donor graft are only delivered to us after earlier uncomplicated kidney or heart transplant to different recipients.
A disadvantage is the small number of available donor grafts. Some patients may need to wait for months.
Fixation of the graft
The firm fixation of the replacement cruciate ligament to the bone is one of the main factors determining the stability and thus the success of ACL grafts in the immediate postoperative phase. Any limitations to postoperative rehabilitation are determined by the strength of the fixation more than by the tear resistance of the graft itself.
We only use the latest fixation methods with high biomechanical pull-out strength, which permit early functional mobilization independent of the graft.
The internationally recognized standard method is still the fixation of the patellar tendon graft with interference screws (as described by Professor Kurosaka in 1987). Occasionally, grafts can be fixed in place using the press-fit method (jamming the bone plug into the drill hole), thus eliminating the need for a screw. By now, numerous other fixation methods with even greater primary pull-out strength are available, which irespective of the type of graft permit the speedy and efficient rehabilitation of athletes.
Grants are either fixed directly using interference screws or indirectly by external fixation methods or a combination of the two.
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Various grafts and fixation techniques for ACL replacements a. Patellar tendon b. Quadruple hamstring c. Quadriceps tendon |
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| a. | b. | c. | |
In conclusion, each type of graft and each method of fixation has its own inherent advantages and disadvantages; the final decision must rest with the experienced surgeon in each individual case as to which material is the best option for a particular patient. There is a clear trend, though, that patients whose work involves kneeling or who suffer from pain in the patellar region should buy preference be fitted with a popliteal rather than a patellar tendon graft.
The long-term results for methods are comparable. The availability of donor tendons is limited; for that reason, they are these days only chosen for repeat operations or multiple complex ligament injuries. Plastic tendons have not proven to be worthwhile in the medium and long-term.
Technique: Fully arthroscopic cruciate ligament surgery
In contrast with the large opening of the knee joint still practised elsewhere, we consistently use arthroscopic surgical methods because the arthroscopic camera permits inspection of the entire interior particular space. Using micro-instruments, the joint is prepared for accepting the graft. There is no need at all to open the joint with a commensurately large incision; all that is required for the arthroscopic procedure are two small incisions of about 8 mm each. The graft is then harvested. Specially developed precision instruments permit the anatomically exact and arthroscopically verifiable siting of the graft. Correct application of this surgical technique requires professional experience of the highest level. For this reason, a specialized centre such as the Centre for Orthopaedic Surgery Pfaeffikon, Schwyz is much better placed to carry out such a procedure routinely and with a much greater prospect of success.
Arthroscopically controlled insertion of the graft with subsequent fixation
using bioresorbable screws (illustration of a patellar tendon graft).
Rehabilitation following ACL reconstruction
Rehabilitation of the anterior cruciate ligament is still a topic of great interest both to orthopaedic surgeons and physiotherapists. Numerous experimental studies have shown that movement and a certain enforced strain are crucial for the healing of the ligament. The formation of new collagen and the reorganization of the graft has been confirmed and proven.
Other experimental and clinical studies have underlined the particular advantage of closed-chain rehabilitation exercises as opposed to open-chain ones for placing strain on the ACL. An example of open-chain mobility is the free movement of the lower leg in the swing phase of running or when exercising with a leg curler. Conversely, closed-chain mobility involves the foot having contact with and transmitting power to the base (cycling, leg press). Strain measurements have shown that the force exerted on the ACL is 5 to 17 times higher in open-chain exercises than in closed-chain ones.
Immobilizing the joint in plaster for four weeks has been shown to result in a dramatic reduction of the graft's tear resistance and insufficient restoration of its biomechanic functionality. Six weeks of immobilisation in plaster also cause the quadriceps muscle to lose 30-40% of its isometric strength, 20-30% of its cross-section and 10-20 % of its girth. The tear resistance of the graft is greatest at the time of surgery (implantation); for this reason, the chances of early mobilisation and enforced rehabilitation in the first six weeks depend on the pull-out strength of the fixation of the graft to the bone. Studies have shown that the ACL is daily exposed to forces of up to 700 Newton, e.g. when decelerating from jogging. Sporting activities can result in even higher exposures to strain.
Forces on the anterior cruciate ligament during normal daily activities
(according to Rosenberg and de Paulos)
It can therefore be concluded that normal walking, semi-knee-bends with an inclined upper body and leg press exercises in the early postoperative phase do not result in loosening, but on the contrary contribute also in the long-term to improved stability of the anterior cruciate ligament. For this reason, the main focus should be on full extension of the knee in the immediately postoperative phase in order to avoid any extension deficit.